Cable made from crosslinkable composition without antioxidant and with beneficial methane formation

ABSTRACT

The invention relates to a cable comprising layer(s), which layer(s), is/are obtained from a polymer composition, wherein the polymer composition comprises a polyethylene and a crosslinking agent, wherein the polymer composition contains a total amount of vinyl groups which is B vinyl groups per 1000 carbon atoms, and B1≤B, wherein B1 is 0.88, when measured prior to crosslinking according to method ASTM D6248-98; and wherein the crosslinking agent is present in an amount which is Z wt %, prior to crosslinking, based on the total amount (100 wt %) of the polymer composition, and Z≤Z2, wherein Z2 is 0.60, the cable, e.g. being a power cable, and processes for producing the cable; the cable useful in different end applications, such as wire and cable (W&amp;C) applications.

FIELD OF INVENTION

The invention relates to a cable comprising layer(s), which layer(s)is/are obtained from a polymer composition, wherein the polymercomposition comprises a polyethylene and a crosslinking agent, the cablemay be a power cable, and a process for producing a cable whichcomprises use of a polymer composition. Further, the cable applications,may be power cable applications, e.g., in medium voltage (MV) and, forexample, in high voltage (HV) and, for example, e.g., extra high voltage(EHV) cable applications. Further, the cable may be useful in bothalternating current (AC) and direct current (DC) applications.

BACKGROUND ART

Polyethylenes produced in a high pressure (HP) process are widely usedin demanding polymer applications wherein the polymers must meet highmechanical and/or electrical requirements. For instance in wire andcable (W&C) applications, e.g. power cable applications, e.g., in lowvoltage (LV), MV, HV and EHV applications, the mechanical and theelectrical properties of polyethylenes, and of polymer compositionscomprising polyethylenes, have significant importance.

For instance in power cable applications, particularly in MV andespecially in HV and EHV cable applications, the electrical propertiesof the polymer composition have a significant importance. Furthermore,the electrical properties, which are of importance, may differ indifferent cable applications, as is the case between AC and DC cableapplications.

Further, it is also known that crosslinking of polymers, e.g.polyethylenes, substantially contributes to an improved heat anddeformation resistance, mechanical strength, chemical resistance andabrasion resistance of a polymer.

Therefore crosslinked polymers are widely used in different endapplications, such as in the mentioned W&C applications.

Furthermore, in cable applications, an electric conductor is usuallycoated first with an inner semiconducting layer, followed by aninsulating layer and an outer semiconducting layer. To these layers,additional layer(s) may be added, such as screen(s) and/or auxiliarybarrier layer(s), e.g. one or more water barrier layer(s) and one ormore jacketing layer(s).

Due to benefits, mentioned herein, which are achievable withcrosslinking, the insulating layer and the semiconducting layers incable applications are typically made using crosslinkable polymercompositions. The polymer compositions in a formed layered cableapplication are then crosslinked.

Furthermore, such crosslinkable polymer compositions comprising lowdensity polyethylene (LDPE), are today among the predominant cableinsulating materials for power cables.

The crosslinking can be performed with crosslinking agents where thecrosslinking agents decompose generating free radicals. Suchcrosslinking agents, e.g. peroxides, are conventionally added to thepolymeric material prior to, or during, the extrusion of the cable. Saidcrosslinking agent should preferably remain stable during the extrusionstep. The extrusion step should preferably be performed at a temperaturelow enough to minimize the early decomposition of the crosslinkingagent, but high enough to obtain proper melting and homogenisation ofthe polymer composition. If a significant amount of crosslinking agent,e.g. peroxide, decomposes already in the extruder, and thereby initiatespremature crosslinking, it will result in formation of, so-called,“scorch”, i.e. inhomogeneity, surface unevenness and possiblydiscolouration in the different layers of the resultant cable.Therefore, any significant decomposition of crosslinking agents, i.e.free radical forming agents, during extrusion should be avoided.Instead, the crosslinking agents should ideally decompose merely in asubsequent crosslinking step at elevated temperature. The elevatedtemperature will increase the decomposition rate of the crosslinkingagents and will thus increase crosslinking speed, and a desired, i.e. atarget, crosslinking degree may be reached faster.

Moreover, when a polymer composition in, for example, a cable, iscrosslinked, the decomposition of the crosslinking agents, e.g.peroxides, during the crosslinking, will further also result information of peroxide decomposition products. Some of the peroxidedecomposition products are volatile, and their main component is methaneif the types of peroxides that typically are used for crosslinking inrelation to, for example, a cable, are used. The peroxide decompositionproducts remain mostly captured within the polymer composition of, forexample, a cable, after crosslinking. This causes, e.g. problems in viewof the cable manufacturing process as well as in view of the quality ofthe final cable.

Especially MV, HV, and EHV power cables must have layers of high qualityin order to help safety during installation and in end uses of saidcables. In installation, for example, it is of importance to avoid thatcaptured decomposition products e.g. flammable methane, ingnite, forexample when end caps are removed. In service, volatile peroxidedecomposition products formed in a cable during a crosslinking step cancreate a gas pressure and thus cause defects in the shielding and in thejoints. E.g. when a cable core is equipped with a metal barrier, thenthe gaseous products can exert a pressure, especially on the joints andterminations, whereby a system failure may occur. Thus, the level ofthese volatile peroxide decomposition products needs to be reduced, to alow enough level, before subsequent cable production steps can takeplace.

A low enough level of the volatile peroxide decomposition productsrenders a use of the polymer composition comprising LDPE safe for use ininstallations, such as cable installations, and with accessories, suchas cable accessories. Thus, today a, so called, degassing step, whichreduces the level of volatile peroxide decomposition products, is neededin cable production process. The degassing step is a time and energyconsuming and thus costly operation in a cable manufacturing process.

Degassing requires large heated chambers which must be well ventilatedto avoid the build-up of e.g. flammable methane. The cable core, i.e.layers and conductor, typically wound onto cable drums, is normally heldin said degassing step in elevated temperature in the range of 50-80°C., e.g. 60-70° C., for lengthy time periods. When exposed to therequired temperatures thermal expansion and softening of the insulationcan occur and lead to unwanted deformation of the formed cable layersresulting directly to failures of the cable. The degassing of HV and EHVcables with high cable weight needs thus often to be carried out atdecreased temperatures which prolongs the degassing time further.Accordingly, there is a need to find new solutions to overcome theproblems of the state of the art.

Further, the crosslinking of a polymer composition, comprised, in, forexample, a cable, substantially contributes, to the improved heat anddeformation resistance, mechanical strength, chemical resistance andabrasion resistance of the polymer composition and the cable comprisingthe polymer composition.

In this context see U.S. Pat. No. 5,539,075, which relates to a methodof producing an unsaturated copolymer of ethylene and at least onemonomer, wherein the monomer is a polyunsaturated compound andcopolymerisable with ethylene.

See also EP2318210B1, which relates to a polymer composition comprisingan unsaturated LDPE copolymer of ethylene with one or morepolyunsaturated comonomers and being suitable for crosslinked polymerapplications. The polymer composition has a melt flow rate under 2.16 kgload, MFR₂, of at least 2.8 g/10 min, and contains carbon-carbon doublebonds in an amount of at least 0.40 carbon-carbon double bonds/1000carbon atoms.

Additionally, different materials, i.e. polymer compositions, may beneeded for different cables, cable constructions and lines. Moreover, itis not possible to run all cables or cable constructions on all cablelines using, a, herein so called, standard viscosity “crosslinked”(here, more correctly, meaning “crosslinkable”) polyethylene (XLPE)materials having melt flow rate under 2.16 kg load, MFR₂, values around2 g/10 min. That is because of that these standard viscosity XLPEmaterials do not have sufficient sagging resistance. The insufficiencyin sagging resistance is normally solved, in the case of a cable, byusing materials with MFR₂ values lower than 2 g/10 min. Materials, whichhave MFR₂ values lower than 2 g/10 min, have high viscosity and improvedsagging resistance. The improved sagging resistance is needed for bigcable constructions and for cable production in catenary cable lines, aswell as, for cable production in horizontal cable lines. For example, inhorizontal continuous vulcanization lines, e.g. a Mitsubishi DainichiContinuous Vulcanization (MDCV) line, and in catenary continuousvulcanization (CCV) lines (especially for thicker constructions) forproducing cables, it is typically required to use polymeric materials,e.g., for insulation layers, which have lower MFR₂ compared to the MFR₂of polymeric materials (e.g. standard viscosity XLPE materials) used invertical continuous vulcanization (VCV) lines and CCV lines (for thinnerconstructions).

In horizontal continuous vulcanization lines for producing cables, theconductor may sink within the insulation layer, if polymeric materialswhich have a too high MFR₂ are used, the sinking of the conductor mayalso result in an eccentricity of the cable core.

Likewise in CCV lines, if polymeric materials which have a too highMFR₂, i.e. also having a too low sagging resistance, are used, the wallthickness may become too large as soft molten polymeric material of aninsulation layer may drop off the conductor. This will result in adownward displacement of the insulation layer, thus rendering aneccentricity, e.g. a, so called, pear shaped cable core.

Further, the insufficiency in the sagging resistance may be counteractedby different methods, such as:

-   -   using eccentric tools in the extruder head to compensate for the        effect of sinking of the conductor;    -   twisting of the cable core to counter act displacement of the        conductor, using of a double rotating technique to counteract        the pear shaping, and, also, using a, so-called, entry heat        treatment (EHT).

Accordingly, polymeric materials having a comparably lower MFR₂ andhigher viscosity, as already described, are normally used to counteractthese sagging behaviors.

However, materials having high viscosity will generate a higher melttemperature at commonly used extrusion conditions which may lead tohigher risk for premature crosslinking and, thus, formation ofprematurely crosslinked matter, i.e. “scorch”. “Scorch” may, as alreadydescribed herein, be inhomogeneity, surface unevenness and/or possiblydiscolouration in the different layers of, for example, the resultingcable. The formation of “scorch” may have severe impact onproductivities in the cable lines, as it significantly limits theproduction length before cleaning is needed and therefore the productionrate is reduced. Thus, when producing a cable, by using polymericmaterials having a lower MFR₂ generating a higher temperature in themelt, a lower production speed is required to reduce the melttemperature and thereby minimizing “scorch”.

Accordingly, a drawback with decreasing the MFR₂ value of a material maythus be that it also requires changes in processing conditions such asthe lowering of the production speed.

The processing conditions are, besides the sagging resistance, alsoproperties that are of importance in relation to crosslinkable XLPEmaterials, such as peroxide crosslinkable XLPE materials. Ideally, thematerial shall have low viscosity under the extrusion step of theprocess in order to have an, under the extrusion step, desirably lowmelt temperature. On the other hand, in the crosslinking step of theprocess a comparably higher viscosity of the material may be desirable.If a crosslinkable XLPE material generates a low melt temperature, thereis less risk for “scorch” formation during an extrusion of, e.g., acable construction, as compared with an extrusion involving anothercrosslinkable XLPE material generating a higher temperature in the melt.

The sagging resistance and the viscosity under processing conditions mayboth be visualised by viscosity curves obtained in plate-plate rheologymeasurements. Said sagging resistance is, then, visualised via thecomplex viscosity (η*) at very low shear rates, i.e. η*₀ and η*_(0.05)at 0 rad/sec and 0.05 rad/sec, respectively, and said viscosity underprocessing conditions is, then, visualised via the complex viscosityη*₃₀₀ at 300 rad/sec.

Still a further important property for XLPE is the crosslinking degreewhere the target crosslinking degree level shall be reached with,ideally, as low amount of crosslinking agent, such as peroxide, aspossible. The degree of crosslinking may, for example, be measured withthe, so-called, hot set test. In accordance with said hot set test, thelower the hot set elongation value, the more crosslinked is thematerial. An, as low as possible, amount of the crosslinking agentreduces the volatile peroxide decomposition products and also reducestime needed for degassing.

The extrusion and the crosslinking steps of a polymeric materialincluded in, for example, cable production have different requirements.The critical parameter for the extrusion step is, as already described,that the polymeric material generates a low melt temperature in order toreduce the risk for “scorch”. This is influenced by the rheologicalproperties in the region of shear rate that the polymeric material isexhibiting in the extruder, for example, using a low complex viscosity(η*) at 300 rad/sec. A low complex viscosity (η*) at 300 rad/sec isgenerally connected to a polymeric material having a higher melt flowrate (MFR₂).

However, an increase in melt flow rate must often be balanced as apolymeric material with a high MFR₂ has a too low sagging resistancewhich will result in, for example, a non-centric cable, which is notacceptable. The rheological property that is influencing the saggingresistance is the complex viscosity (η*) at very low shear rates, suchas, at 0 rad/sec. However, the complex viscosity (η*) at 0 rad/sec is anextrapolated value, and thus here a measured complex viscosity (η*) at0.05 rad/sec is used instead.

Accordingly, there is a need to find new solutions to overcome theproblems of the state of the art.

DESCRIPTION OF THE INVENTION

The present invention relates to a cable comprising layer(s), whereinlayer(s), is/are obtained from a polymer composition, wherein thepolymer composition comprises a polyethylene and a crosslinking agent,wherein the polymer composition contains a total amount of vinyl groupswhich is B vinyl groups per 1000 carbon atoms, and B₁≤B, wherein B₁ is0.88, when measured prior to crosslinking according to method ASTMD6248-98; and the crosslinking agent is present in an amount which is Zwt %, prior to crosslinking, based on the total amount (100 wt %) of thepolymer composition, and Z≤Z₂, wherein Z₂ is 0.60.

In one embodiment, the inventors have found that the combination of theabove-mentioned features with a relatively low MFR₂ surprisingly leadsto a cable with attractive properties as discussed below.

The cable according to the present invention with layer(s) obtained fromthe polymer composition which contains the comparably higher totalamount of vinyl groups, B, as defined herein, surprisingly combines, inone cable:

good processability, e.g. a good flowability, which is generally onlyassociated with materials having a comparably higher MFR₂, with

excellent sagging resistance generally only associated with materialshaving a comparably lower MFR₂, and

exhibition of surprisingly low methane levels, with

a technically desirable level of crosslinking degree maintained.

Further, that the cable with layer(s) obtained from the polymercomposition combines excellent sagging resistance with goodprocessability, e.g. flowability, is also illustrated by the fact thatthe polymer composition exhibits balanced complex viscosities (η*) at300 rad/sec and at 0.05 rad/sec, both complex viscosities (η*) aredetermined prior to crosslinking according to method ISO 6721-1 onstabilised samples of the polyethylene. The complex viscosity (η*) at300 rad/sec is accordingly low, and the complex viscosity (η*) at 0.05rad/sec is accordingly high, which results in a polymer composition andthus in a cable, according to the present invention, which has improvedprocessing properties in an extruder, and which still allows generationof a cable, including big cable constructions, with good centricity incable production for all types of cable lines. Such cables, comprisinglayer(s), e.g. insulation layer(s), being obtained from the polymercomposition, may thus accordingly be produced.

Moreover, the cable with layer(s) obtained from the polymer composition,according to the present invention, has unexpectedly also been shown toexhibit surprisingly low methane levels, while, at the same time, atechnically desirable level of crosslinking degree, of the polymercomposition and thus of the cable, is maintained using a relatively lowamount of the crosslinking agent, i.e. Z wt %, as defined herein. Thetechnically desirable level of crosslinking degree insures sufficientthermo-mechanical properties, e.g. maintaining dimensional stability atelevated temperature. The crosslinking agent may, e.g., be peroxideswhich are well known in the art. The amount of formed volatiledecomposition products, wherein the main component typically is methane,depends directly on the amount of crosslinking agent, e.g., peroxide,being added to the polymer composition. For any given crosslinkingagent, e.g. peroxide, the amount of formed volatile decompositionproducts further also depends on the chemical structure of thecrosslinking agent. Further, by selecting said relatively low amount ofthe crosslinking agent, while the desirable level of crosslinking degreeof a polymer composition is maintained, a polymer composition and thus acable exhibiting low methane levels, as well as, retaining a memoryeffect when crosslinked, is enabled.

Said low methane levels allow for shorter degassing time or,alternatively, make the degassing step completely redundant, bothalternatives being much benficial for the overall production ofcrosslinkable and crosslinked cables comprising layer(s), e.g. aninsulation layer, obtained from the polymer composition.

Thus, the cable, which may be a crosslinkable or crosslinked cable,comprises layer(s), for example, insulation layer(s), obtained from thepolymer composition comprising the polyethylene is clearly highlyadvantageous.

In an embodiment of the present invention a cable is provided, whereinthe cable comprises one layer being obtained from said polymercomposition.

Embodiments of the cable of the present invention are disclosed, whereinthe layer(s) comprises both layer(s), which is/are obtained from saidpolymer composition, as well as, further layer(s) which is/are obtainedfrom semiconducting composition(s).

Note that the wordings “embodiment” or “embodiments”, even if standingalone herein, always relate embodiment of the present invention orembodiments of the present invention.

The polymer composition is crosslinkable and is highly suitable forproducing the cable, e.g. one or more crosslinkable layers of the cable,for example one or more crosslinkable insulation layers, of the cable,which layers are subsequently crosslinked.

“Crosslinkable” is a well known expression and means that the polymercomposition can be crosslinked, e.g. via radical formation, to formbridges i.a. amongst the polymer chains.

The polymer composition comprises a polyethylene and a crosslinkingagent.

The polyethylene will be described in detail under the section “Thepolyethylene of the polymer composition”.

The polyethylene comprised in the polymer composition may be unsaturatedor saturated.

A further embodiment of the present invention is provided wherein thepolyethylene is saturated.

In a further embodiment the polyethylene is unsaturated.

That the polyethylene is “unsaturated” means herein that thepolyethylene comprises carbon carbon double bonds. Carbon carbon doublebonds mean herein unsaturations. The polyethylene, as described herein,comprises vinyl groups, for example, allyl groups. Vinyl groups arefunctional groups which comprise carbon carbon double bonds. The term“vinyl group” as used herein takes is conventional meaning, i.e. themoiety “—CH═CH₂”. Further, the polyethylene may in addition compriseother functional groups also comprising carbon carbon double bonds. Theother functional groups, also comprising carbon carbon double bonds, maybe, e.g., vinylidene groups and/or vinylene groups. The vinylene grouphas either a cis or trans configuration. For the avoidance of doubt,vinylidene groups and vinylene groups are not vinyl groups as the termsare used herein.

A cable according to the present invention is disclosed, wherein thepolymer composition contains a total amount of vinyl groups which is Bvinyl groups per 1000 carbon atoms, and B₁≤B, wherein B₁ is 0.88, whenmeasured prior to crosslinking according to method ASTM D6248-98.

Said “total amount of vinyl groups which is B vinyl groups per 1000carbon atoms” means the “total amount of vinyl groups which is B vinylgroups per 1000 carbon atoms” present in the polymer composition whenmeasured prior to crosslinking in accordance with the present invention.Further, at least the polyethylene contains said vinyl groups whichcontribute to the total amount of vinyl groups.

The polymer composition may optionally comprise further component(s)containing vinyl groups, which then also contribute to the total amountof said vinyl groups. In an embodiment therefore, the vinyl groupcontent is thus measured on the polymer composition as a whole and notjust on the polyethylene thereof.

The method ASTM D6248-98 for determining the amount of the vinyl groupsare described under “Determination Methods”.

Still a further embodiment according to the present invention, asdescribed herein, discloses a cable, wherein the polymer compositioncontains a total amount of vinyl groups which is B vinyl groups per 1000carbon atoms, and B₁≤B, wherein B₁ is 0.89, when measured prior tocrosslinking according to method ASTM D6248-98.

Still a further embodiment is disclosed, wherein B₁ is 0.90.

In a further embodiment is B₁ 0.92.

An even further embodiment is disclosed, wherein B₁ is 0.94.

Still a further embodiment is disclosed, wherein B₁ is 0.95.

An even further embodiment is disclosed, wherein B₁ is 1.00.

Further embodiments are disclosed, wherein B₁ is 0.95, 1.00, 1.05 or1.10.

Still further embodiments are disclosed, wherein B₁ is 0.95, 1.00, 1.05,1.10, 1.15, 1.20, 1.25 or 1.30.

Even further embodiments are disclosed, wherein B₁ is 1.15, 1.20, 1.25or 1.30.

Still a further embodiment is disclosed, wherein B₁ is 1.30.

Still a further embodiment, as described herein, is disclosed, whereinB≤B₂ and B₂ is 3.0.

Further embodiments are disclosed wherein the polymer compositioncontains a total amount of vinyl groups which is B vinyl groups per 1000carbon atoms, and B₁≤B≤B₂, wherein B₁ and B₂ may each be selected fromany of the values given herein for B₁ and B₂, respectively.

A further embodiment, as described herein, is disclosed, wherein B₂ is2.5.

In a particularly preferred embodiment, B₁ is 0.89 and B₂ is 3.0, evenmore preferably B₁ is 0.90 and B₂ is 1.5.

The polymer composition further comprises a crosslinking agent.

The crosslinking agent, for example a peroxide, is present in an amountwhich is Z wt %, prior to crosslinking, based on the total amount (100wt %) of the polymer composition, and Z≤Z₂, wherein Z₂ is 0.60.

In a further embodiment according to the present invention, thecrosslinking agent is present in an amount which is Z wt %, prior tocrosslinking, based on the total amount (100 wt %) of the polymercomposition, and Z₁≤Z, wherein Z₁ is 0.01.

The crosslinking agent is defined herein to be any compound capable togenerate radicals which can initiate a crosslinking reaction. Forexample, the crosslinking agent contains —O—O— bond.

A further embodiment, as described herein, is disclosed, wherein thecrosslinking agent comprises peroxide, e.g. a peroxide.

In a further embodiment, the crosslinking agent comprises peroxide, i.e.comprises at least one peroxide unit per molecule of crosslinking agent.

In an even further embodiment, the crosslinking agent comprises aperoxide.

In a further embodiment, the crosslinking agent is a peroxide.

In further embodiments of the present invention, a cable, as describedherein, is disclosed, wherein Z₁ is 0.02, 0.04, 0.06 or 0.08.

Even further, embodiments of the present invention, as described herein,are disclosed, wherein Z₁ is, for example, 0.1 or 0.2 and/or Z₂ is, forexample, 0.58 or 0.56.

Further embodiments are disclosed, wherein Z₂ is 0.58, 0.56, 0.54, 0.52,0.50, 0.48, 0.46, 0.44, 0.42 or 0.40.

Still further embodiments are disclosed, wherein Z₂ is 0.58, 0.56, 0.54,0.52 or 0.50.

Even further embodiments are disclosed, wherein Z₂ is 0.48, 0.46, 0.44,0.42 or 0.40.

In a further embodiment Z₂ is 0.58 or 0.56. In still a furtherembodiment Z₂ is 0.58. In an even further embodiment Z₂ is 0.56. In afurther embodiment Z₂ is 0.54, 0.52 or 0.50. In still a furtherembodiment Z₂ is 0.54. In an even further embodiment Z₂ is 0.52. In afurther embodiment Z₂ is 0.50.

In a further embodiment Z₂ is 0.48 or 0.46. In still a furtherembodiment Z₂ is 0.48. In an even further embodiment Z₂ is 0.46.

A further embodiment according to the present invention, as describedherein, is disclosed, the amount Z of the crosslinking agent, forexample a peroxide, is Z₂ being 0.45.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Z₂ is 0.44 or 0.42.

In still a further embodiment the amount Z of the crosslinking agent,for example a peroxide, is Z₂ being 0.40.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Z₂ is 0.38 or 0.36.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Z₂ is 0.38.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Z₂ is 0.36.

In an even further embodiment, the amount Z of the crosslinking agent,for example a peroxide, is Z₂ being 0.35.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Z₂ is 0.34, 0.32 or 0.30.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Z₂ is 0.34.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Z₂ is 0.32.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Z₂ is 0.30.

Non-limiting examples of the crosslinking agents comprise organicperoxides, such as di-tert-amylperoxide,2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3,2,5-di(tert-butylperoxy)-2,5-dimethylhexane, tert-butylcumylperoxide,di(tert-butyl)peroxide, dicumylperoxide,butyl-4,4-bis(tert-butylperoxy)-valerate,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane,tert-butylperoxybenzoate, dibenzoylperoxide, bis(tertbutylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane,1,1-di(tert-butylperoxy)cyclohexane, 1,1-di(tert amylperoxy)cyclohexane,or any mixtures thereof.

In further embodiments, the crosslinking agent being a peroxide may, forexample, be selected from 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3,2,5-di(tert-butylperoxy)-2,5-dimethylhexane,di(tert-butylperoxyisopropyl)benzene, dicumylperoxide,tert-butylcumylperoxide, di(tert-butyl)peroxide, or any mixturesthereof.

In still a further embodiment the crosslinking agent is a peroxideselected from any of dicumylperoxide,2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3 andtert-butylcumylperoxide, or of any mixtures thereof.

In a further embodiment, the crosslinking agent comprises a peroxidewhich is dicumylperoxide.

In still a further embodiment, the crosslinking agent comprises aperoxide which is 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3.

In even a further embodiment, the crosslinking agent comprises aperoxide which is tert-butylcumylperoxide.

In an embodiment the polymer composition comprises the crosslinkingagent.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein B≤B₂ and B₂ is 3.0 and Z₁≤Z≤Z₂,wherein Z₁ is 0.01.

Further embodiments are disclosed, as described herein, wherein thecrosslinking agent is present in an amount which is Z wt %, prior tocrosslinking, based on the total amount (100 wt %) of the polymercomposition, and Z₁≤Z≤Z₂, wherein Z₁ and Z₂ may each be selected fromany of the values given herein for Z₁ and Z₂, respectively.

In a further embodiment according to the present invention, as describedherein, Z₁ is 0.05.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Z₁ is 0.10.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Z₂ is 0.15.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Z₂ is 0.20.

In a particularly preferred embodiment, Z₁ is 0.15 and Z₂ is 0.60, evenmore preferably Z₁ is 0.25 and Z₂ is 0.50.

The MFR₂ is determined, prior to crosslinking, according to ISO1133-1:2011 under 2.16 kg load and at 190° C.

In a further embodiment according to the present invention, the polymercomposition, as described herein, has prior to crosslinking a melt flowrate at 2.16 kg loading (MFR₂) and at 190° C., determined, according tomethod ISO 1133-1:2011, which MFR₂ is A g/10 min and A≤A₂, wherein A₂ is10.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein A₂ is 5.0.

In still a further embodiment of the polymer composition, A₂ is 4.0.

Still an embodiment according to the present invention, as describedherein, is disclosed, wherein A₂ is 3.0.

In still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein A₂ is 2.7.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein A₂ is 2.5.

Still an embodiment according to the present invention, as describedherein, is disclosed, wherein A₂ is 2.0.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein A₂ is 1.7.

In still a further embodiment the polymer composition has a melt flowrate, MFR₂, which is A g/10 min and A₁≤A; wherein A₁ is 0.05.

Further embodiments are disclosed which have a melt flow rate, MFR₂,which is A g/10 min and A₁≤A≤A₂; wherein A₁ and A₂ may each be selectedfrom any of the values given herein for A₁ and A₂, respectively.

Still an embodiment according to the present invention, as describedherein, is disclosed, wherein A₁ is 0.10.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein A₁ is 0.15.

An embodiment according to the present invention, as described herein,is disclosed, wherein A₁ is 0.20.

Still an embodiment according to the present invention, as describedherein, is disclosed, wherein A₁ is 0.25.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein A₁ is 0.30.

An embodiment according to the present invention, as described herein,is disclosed, wherein A₁ is 0.35.

Still an embodiment according to the present invention, as describedherein, is disclosed, wherein A₁ is 0.40.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein A₁ is 0.45.

An embodiment according to the present invention, as described herein,is disclosed, wherein A₁ is 0.50.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein A₁ is 0.55.

An embodiment according to the present invention, as described herein,is disclosed, wherein A₁ is 0.60.

Still an embodiment according to the present invention, as describedherein, is disclosed, wherein A₁ is 0.65.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein A₁ is 0.70.

An embodiment according to the present invention, as described herein,is disclosed, wherein A₁ is 0.75.

Still an embodiment according to the present invention, as describedherein, is disclosed, wherein A₁ is 0.80.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein A₁ is 0.85.

An embodiment according to the present invention, as described herein,is disclosed, wherein A₁ is 0.90.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein A₂ is 1.65.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein A₂ is 1.60.

An embodiment according to the present invention, as described herein,is disclosed, wherein A₂ is 1.55.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein A₂ is 1.50.

In a particularly preferred embodiment, A₁ is 0.15 and A₂ is 3.0, evenmore preferably A₁ is 0.60 and A₂ is 2.5.

In one preferred embodiment the polymer composition simultaneouslysatisfies the following:

-   -   B₁≤B≤B₂ wherein B₁ is 0.89 and B₂ is 3.0;    -   Z₁≤Z≤Z₂ wherein Z₁ is 0.15 and Z₂ is 0.60; and    -   A₁≤A≤A₂ wherein A₁ is 0.15 and A₂ is 3;

preferably

-   -   B₁≤B≤B₂ wherein B₁ is 0.9 and B₂ is 1.5;    -   Z₁≤Z≤Z₂ wherein Z₁ is 0.25 and Z₂ is 0.50; and    -   A₁≤A≤A₂ wherein A₁ is 0.60 and A₂ is 2.5.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein the polyethylene, before crosslinking, hasa complex viscosity (η*) at 0.05 rad/sec, which is X Pas, and X₁≤X≤X₂,

wherein X₁ is 7600 and X₂ is 30000, and

a complex viscosity (η*) at 300 rad/sec, which is Y Pas, and Y₁≤Y≤Y₂,wherein Y₁ is 5 and Y₂ is 380, both complex viscosities (η*) aredetermined according to method ISO 6721-1 on stabilised samples of thepolyethylene.

Further embodiments are disclosed wherein the polyethylene, beforecrosslinking, has a complex viscosity (η*) at 0.05 rad/sec, determinedaccording to method ISO 6721-1 on stabilised samples of thepolyethylene, which is X Pas, and X₁≤X≤X₂, wherein X₁ and X₂ may each beselected from any of the values given herein for X₁ and X₂,respectively.

Still further embodiments are disclosed wherein the polyethylene, beforecrosslinking, has a complex viscosity (η*) at 300 rad/sec determinedaccording to method ISO 6721-1 on stabilised samples of thepolyethylene, which is Y Pas, and Y₁≤Y≤Y₂, wherein Y₁ and Y₂ may each beselected from any of the values given herein for Y₁ and Y₂,respectively.

An embodiment to the present invention, as described herein, isdisclosed, wherein X₁ is 7614.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₁ is 8000.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 9000.

An embodiment according to the present invention, as described herein,is disclosed, wherein X₁ is 10000.

An embodiment according to the present invention, as described herein,is disclosed, wherein X₁ is 11000.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₁ is 12000.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 13000.

An embodiment according to the present invention, as described herein,is disclosed, wherein X₁ is 14000.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₂ is 29000.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₂ is 28000.

An embodiment according to the present invention, as described herein,is disclosed, wherein X₂ is 27000.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₂ is 26000.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₂ is 25000.

An embodiment according to the present invention, as described herein,is disclosed, wherein X₂ is 24000.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₁ is 15000.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 16000.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₁ is 17000.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 18000.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₁ is 18100.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 18200.

An embodiment according to the present invention, as described herein,is disclosed, wherein X₁ is 18300.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₁ is 18400.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 18500.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₁ is 18600.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 18700.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₂ is 23500.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₂ is 23000.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₂ is 22900.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₂ is 22800.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₂ is 22700.

An embodiment according to the present invention, as described herein,is disclosed, wherein X₂ is 22600.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₂ is 22500.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₂ is 22400.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₂ is 22300.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₁ is 10.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 20.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₁ is 30.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 40.

An embodiment according to the present invention, as described herein,is disclosed, wherein Y₁ is 50.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₁ is 60.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 70.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₁ is 80.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 90.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₁ is 100.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 110.

An embodiment according to the present invention, as described herein,is disclosed, wherein Y₁ is 120.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₁ is 130.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 140.

An embodiment according to the present invention, as described herein,is disclosed, wherein Y₁ is 150.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₁ is 160.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 170.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₁ is 180.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 190.

An embodiment according to the present invention, as described herein,is disclosed, wherein Y₁ is 200.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₁ is 210.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 220.

An embodiment according to the present invention, as described herein,is disclosed, wherein Y₁ is 230.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₁ is 240.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 250.

An embodiment according to the present invention, as described herein,is disclosed, wherein Y₂ is 378.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₂ is 375.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₂ is 360.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₂ is 355.

An embodiment according to the present invention, as described herein,is disclosed, wherein Y₂ is 350.

Even a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₂ is 345.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein Y₂ is 340.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein Y₂ is 335.

An embodiment according to the present invention, as described herein,is disclosed, wherein Y₂ is 330.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 8000 and X₂ is 28000, andwherein Y₁ is 250 and Y₂ is 360.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein X₁ is 12000 and X₂ is 28000, and whereinY₁ is 250 and Y₂ is 330.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 13000 and X₂ is 27000, andwherein Y₁ is 240 and Y₂ is 340.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 13000 and X₂ is 27000, andwherein Y₁ is 250 and Y₂ is 330.

In further embodiments the polymer composition may also comprise furtheradditive(s). Such further additive(s) comprise:

unsaturated low molecular weight compound(s), for example:

-   -   Crosslinking booster(s) mentioned herein, including any given        specific compound(s), which can contribute to the crosslinking        degree and/or to the amount of vinyl groups in the polymer        composition.    -   One or more scorch retarders (SR) which are defined herein to be        compounds that reduce the formation of scorch during extrusion        of a polymer composition, at typical extrusion temperatures        used, if compared to the same polymer composition extruded        without said compound. The scorch retarders can also contribute        to the total amount of vinyl groups in the polymer composition.

Any contribution from the unsaturated low molecular weight compound(s),for example, the crosslinking booster(s) and/or the “one or more” scorchretarders (SR) to the amount of vinyl groups in the polymer compositionis also measured according to method ASTM D6248-98.

The crosslinking booster may be a compound containing at least 2,unsaturated groups, such as an aliphatic or aromatic compound, an ester,an ether, an amine, or a ketone, which contains at least 2, unsaturatedgroup(s), such as a cyanurate, an isocyanurate, a phosphate, an orthoformate, an aliphatic or aromatic ether, or an allyl ester of benzenetricarboxylic acid. Examples of esters, ethers, amines and ketones arecompounds selected from general groups of diacrylates, triacrylates,tetraacrylates, triallylcyanurate, triallylisocyanurate,3,9-divinyl-2,4,8,10-tetra-oxaspiro[5,5]-undecane (DVS), triallyltrimellitate (TATM) orN,N,N′,N′,N″,N″-hexaallyl-1,3,5-triazine-2,4,6-triamine (HATATA), or anymixtures thereof. The crosslinking booster can be added in an amount ofsuch crosslinking less than 2.0 wt %, for example, less than 1.5 wt %,e.g. less than 1.0 wt %, for example, less than 0.75 wt %, e.g. lessthan 0.5 wt %, and the lower limit thereof is, for example, at least0.05 wt %, e.g., at least 0.1 wt %, based on the weight of the polymercomposition.

The scorch retarders (SR) may, e.g., be unsaturated dimers of aromaticalpha-methyl alkenyl monomers, such as 2,4-di-phenyl-4-methyl-1-pentene,substituted or unsubstituted diphenylethylene, quinone derivatives,hydroquinone derivatives, monofunctional vinyl containing esters andethers, monocyclic hydrocarbons having at least two or more doublebonds, or mixtures thereof. For example, the scorch retarder may beselected from 2,4-diphenyl-4-methyl-1-pentene, substituted orunsubstituted diphenylethylene, or mixtures thereof.

The amount of scorch retarder may, for example, be equal to, or morethan, 0.005 wt %, based on the weight of the polymer composition.Further, the amount of scorch retarder may, for example, be equal to, ormore than, 0.01 wt %, equal to, or more than, 0.03 wt %, or equal to, ormore than, 0.04 wt %, based on the weight of the polymer composition.

Further, the amount of scorch retarder may, for example, be equal to, orless than, 2.0 wt %, e.g., equal to, or less than, 1.5 wt %, based onthe weight of the polymer composition. Further, the amount of scorchretarder may, for example, be equal to, or less than, 0.8 wt %, equalto, or less than, 0.75 wt %, equal to, or less than, 0.70 wt %, or equalto, or less than, 0.60 wt %, based on the weight of the polymercomposition. Moreover, the amount of scorch retarder may, for example,be equal to, or less than, 0.55 wt %, equal to, or less than, 0.50 wt %,equal to, or less than, 0.45 wt %, or equal to, or less than, 0.40 wt %,based on the weight of the polymer composition.

Still further, the amount of scorch retarder may, for example, be equalto, or less than, 0.35 wt %, e.g., equal to, or less than, 0.30 wt %,based on the weight of the polymer composition. Further, the amount ofscorch retarder may, for example, be equal to, or less than, 0.25 wt %,equal to, or less than, 0.20 wt %, equal to, or less than, 0.15 wt %, orequal to, or less than, 0.10 wt %, based on the weight of the polymercomposition. Moreover, the amount of scorch retarder may, for example,be equal to, or less than, 0.15 wt %, or equal to, or less than, 0.10 wt%, based on the weight of the polymer composition.

Furthermore, the amount of scorch retarder may, for example, be withinthe range of 0.005 to 2.0 wt %, e.g., within the range of 0.005 to 1.5wt %, based on the weight of the polymer composition. Furtherexemplified ranges are e.g. from 0.01 to 0.8 wt %, 0.03 to 0.75 wt %,0.03 to 0.70 wt %, or 0.04 to 0.60 wt %, based on the weight of thepolymer composition. Moreover, exemplified ranges are e.g. from 0.01 to0.60, to 0.55, to 0.50, to 0.45 or, alternatively, to 0.40 wt %, 0.03 to0. 0.55 or, alternatively, to 0.50 wt %, 0.03 to 0.45 or, alternatively,0.40 wt %, or 0.04 to 0.45 or, alternatively, 0.40 wt %, based on theweight of the polymer composition.

Further, the scorch retarders (SR) may, e.g., be selected from graftablestable organic free radicals, as described in EP1699882, which includehindered amine-derived stable organic free radicals: for example,hydroxy-derivative of 2,2,6,6,-tetramethyl piperidinyl oxy (TEMPO), e.g.4-hydroxy-TEMPO or a bis-TEMPO (for example,bis(1-oxyl-2,2,6,6-tetramethylpiperidine-4-yl)sebacate), and, forexample, multi-functional molecules having at least two nitroxyl groupsderived from oxo-TEMPO, 4-hydroxy-TEMPO, an ester of 4-hydroxy-TEMPO,polymer-bound TEMPO, PROXYL, DOXYL, ditertiary butyl N oxyl, dimethyldiphenylpyrrolidine-1-oxyl, or 4 phosphonoxy TEMPO.

The graftable stable organic free radicals may be, as described inEP1699882, present in an amount equal to, or more than, about 0.005weight percent, for example, equal to, or more than, about 0.01 weightpercent and equal to, or more than, about 0.03 weight percent, based onthe weight of the polymer composition.

Further, the graftable stable organic free radicals may be, as describedin EP1699882, present in an amount equal to, or less than, about 20.0weight percent, for example, equal to, or less than, about 10.0 weightpercent, e.g., equal to, or less than, about 5.0 weight percent, basedon the weight of the polymer composition.

Furthermore, the graftable stable organic free radicals may be, asdescribed in EP1699882, present in an amount between about 0.005 weightpercent and about 20.0 weight percent, for example, between 15 about0.01 weight percent and about 10.0 weight percent, e.g., between about0.03 weight percent and about 5.0 weight percent, based on the weight ofthe polymer composition.

Moreover, such further additive(s) comprise additive(s), such asantioxidant(s), stabiliser(s), and/or processing aid(s). As anantioxidant, sterically hindered or semi-hindered phenol(s), aromaticamine(s), aliphatic sterically hindered amine(s), organic phosphate(s),thio compound(s), and mixtures thereof, can be mentioned. As furtheradditive(s), flame retardant additive(s), water tree retardantadditive(s), acid scavenger(s), filler(s) pigment(s), and voltagestabilizer(s) can be mentioned.

Examples of suitable fillers and/or pigments include TiO₂, CaCO₃, carbonblack (e.g. conductive carbon black or “UV black”, i.e. a carbon blackthat absorbs ultraviolet radiation), huntite, mica, kaolin, aluminiumhydroxide (ATH), magnesium dihydroxide (MDH), and SiO₂.

In still a further embodiment the polymer composition further comprisesfillers and/or pigments.

Furthermore, said fillers and/or pigments may be comprised in thepolymer composition in amounts of, for example, 0.01 to 5 wt %, e.g.,0.01 to 3 wt % or, e.g., 0.01 to 2 wt %.

The polymer composition may additionally comprise further polymercomponent(s) including unsaturated polymer(s) and/or polymer(s) that arenot unsaturated, wherein the further polymer component(s) are differentfrom said polyethylene.

The polymer composition can be provided in the form of a powder orpellets in any shape and size including granules. Pellets can beproduced, e.g. after polymerisation of said polyethylene, in a wellknown manner using the conventional pelletising equipment, such as apelletising extruder. The polymer composition may, for example, beprovided in the form of pellets.

As already described herein, embodiments of the cable of the presentinvention are disclosed, wherein the layer(s) comprises both layer(s),which is/are obtained from said polymer composition, as well as, furtherlayer(s) which is/are obtained from semiconducting composition(s).

Furthermore, when layer(s) comprising both said layer(s) and saidfurther layer(s), of the cable of the present invention, are crosslinkedthe decomposition of crosslinking agent during the crosslinking, resultsin a content of less than 200 ppm of methane, when measured according tothe method for GC-Analysis, while, at the same time, a technicallydesirable level of crosslinking degree of said layer(s) is maintained,when measured according to the method for Hot Set Determination. Themethod for GC-Analysis and the method for Hot Set Determination aredescribed further herein in the experimental part under “Determinationmethods”.

In an embodiment according to the present invention, a cable, asdescribed herein, is disclosed, comprising layer(s) wherein saidlayer(s) is/are crosslinked, and the decomposition of crosslinking agentduring the crosslinking, results in a content of less than 200 ppm ofmethane, when measured according to the method for GC-Analysis.

In a further embodiment according to the present invention, a cable, asdescribed herein, is disclosed, wherein the decomposition of thecrosslinking agent results in the content of less than 190 or 180 ppm ofmethane.

An embodiment according to the present invention, as described herein,is disclosed, wherein the decomposition of the crosslinking agentresults in the content of less than 170 or 160 ppm of methane.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein the decomposition of the crosslinkingagent results in the content of less than 150 ppm of methane.

An embodiment according to the present invention, as described herein,is disclosed, wherein the decomposition of the crosslinking agentresults in the content of less than 140, 130, 120, 110 or 100 ppm ofmethane.

Still an embodiment according to the present invention, as describedherein, is disclosed, wherein the decomposition of the crosslinkingagent results in the content of less than 115, 110, 105 or 100 ppm ofmethane.

Further, the crosslinked said layer(s) has a hot set elongation, with aload of 20 N/cm², which is less than 175% at 200° C., when measuredaccording to the method for Hot Set Determination. This method isdescribed further herein in the part relating to crosslinking and alsoin the experimental part under “Determination methods”.

An embodiment of a cable according to the present invention, asdescribed herein, is disclosed, wherein said layer(s) is/are crosslinkedand has a hot set elongation, with a load of 20 N/cm², which is lessthan 175%, when measured according to the method for Hot SetDetermination.

In a further embodiment according to the present invention, saidlayer(s), as described herein, has a hot set elongation, with a load of20 N/cm², which is less than 170%, or, alternatively, is less than 160%.

Still an embodiment according to the present invention, as describedherein, is disclosed, wherein said hot set elongation, with a load of 20N/cm², is less than 150%.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein said hot set elongation, with a load of 20N/cm², is less than 140%.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein said hot set elongation, with aload of 20 N/cm², is less than 130%.

An even further embodiment according to the present invention, asdescribed herein, is disclosed, wherein said hot set elongation, with aload of 20 N/cm², is less than 120%, or, alternatively, is less than110%.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein the crosslinked said layer(s) has a hotset elongation, with a load of 20 N/cm², which is less than 100%.

An embodiment according to the present invention, as described herein,is disclosed, wherein the crosslinked said layer(s) has a hot setelongation, with a load of 20 N/cm², which is less than 95%, or,alternatively, is less than 90%.

An embodiment according to the present invention, as described herein,is disclosed, wherein the decomposition of the crosslinking agentresults in the content of less than 150 ppm of methane and thecrosslinked said layer(s) has a hot set elongation, with a load of 20N/cm², which is less than 100%.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein the decomposition of the crosslinkingagent results in the content of less than 150 ppm of methane and thecrosslinked said layer(s) has a hot set elongation, with a load of 20N/cm², which is less than 90%.

The Polyethylene of the Polymer Composition

In embodiments of the present invention, the polyethylene comprised inthe polymer composition contains said total amount of vinyl groups whichis P vinyl groups per 1000 carbon atoms, as described herein. Asdescribed herein P₁≤P or P₁≤P≤P₂.

In an embodiment, the polyethylene contains said total amount of vinylgroups which is P vinyl groups per 1000 carbon atoms.

In a further embodiment, the polyethylene contains the total amount ofvinyl groups being P wherein P₁ is 0.88.

In a particularly preferred embodiment, P₁ is 0.89 and P₂ is 3.0, evenmore preferably P₁ is 0.90 and P₂ is 1.5.

In one preferred embodiment the polymer composition simultaneouslysatisfies the following:

-   -   P₁≤P≤P₂ wherein P₁ is 0.89 and P₂ is 3.0;    -   Z₁≤Z≤Z₂ wherein Z₁ is 0.15 and Z₂ is 0.60; and    -   A₁≤A≤A₂ wherein A₁ is 0.15 and A₂ is 3;    -   preferably    -   P₁≤P≤P₂ wherein P₁ is 0.9 and P₂ is 1.5;    -   Z₁≤Z≤Z₂ wherein Z₁ is 0.25 and Z₂ is 0.50; and    -   A₁≤A≤A₂ wherein A₁ is 0.60 and A₂ is 2.5.

The “amount of vinyl groups” means in this embodiment the “total amountof vinyl groups present in the polyethylene”. The polyethylene meansherein both homopolymer, having been provided with unsaturation by achain transfer agent, and a copolymer, wherein the unsaturation isprovided by polymerising a monomer together with at least apolyunsaturated comonomer, optionally in the presence of a chaintransfer agent and, also, optionally in combination with furthercomonomers.

In one embodiment the polyethylene is an unsaturated copolymer which, asalready mentioned herein, comprises one or more polyunsaturatedcomonomer(s). Further, said vinyl groups (P) present in the unsaturatedcopolymer may originate from said polyunsaturated comonomer, a processof producing the polyethylene and, optionally, from any used chaintransfer agent.

When the polyethylene of the polymer composition, is an unsaturatedcopolymer comprising at least one polyunsaturated comonomer, then thepolyunsaturated comonomer is straight carbon chain with at least 8carbon atoms and at least 4 carbon atoms between the non-conjugateddouble bonds, of which at least one is terminal.

As to suitable polymer materials for the polymer composition, saidpolyethylene can be any polymer having relevant features, as definedherein, for the polyethylene of the exemplified polymer composition. Thepolyethylene may be selected from homopolymers of polyethylene as wellas copolymers of polyethylene with one or more comonomer(s). Thepolyethylene can be unimodal or multimodal with respect to molecularweight distribution and/or comonomer distribution, which expressionshave a well known meaning.

In one embodiment, the polyethylene is a homopolymer of ethylene.

In an embodiment, the polymer composition is obtained by a processcomprising homopolymerisation of ethylene.

In an exemplified embodiment, the polyethylene is an unsaturatedcopolymer of polyethylene with at least one polyunsaturated comonomerand optionally with one or more other comonomer(s).

Said unsaturated copolymer of polyethylene is an unsaturated copolymerof ethylene.

In an embodiment of the present invention, the polyethylene is acopolymer of a monomer with at least one polyunsaturated comonomer andwith zero, one or more, for example, zero, one, two or three, othercomonomer(s), and wherein said total amount of vinyl groups (B) presentin the polymer composition include vinyl groups originating from said atleast one polyunsaturated comonomer, e.g. diene.

In an exemplified embodiment, the polymer composition is obtained by aprocess comprising blending an unsaturated copolymer of ethylene withthe crosslinking agent.

Said copolymer of ethylene may be a LDPE copolymer produced in acontinuous high pressure polymerisation process, wherein ethylene iscopolymerised with at least one polyunsaturated comonomer and optionallywith one or more other comonomer(s), optionally in the presence of achain transfer agent.

The optional further comonomer(s) present in the polyethylene, forexample, copolymer of ethylene, is different from the “backbone” monomerand may be selected from an ethylene and higher alpha-olefin(s), e.g.C₃-C₂₀ alpha-olefin(s), for example, a cyclic alpha-olefin of 5 to 12carbon or a straight or branched chain alpha-olefin of 3 to 12 carbonatoms, such as propylene, 1-butene, 1-hexene, 1-nonene or 1-octene, aswell as, from polar comonomer(s).

In one embodiment the straight or branched chain alpha-olefin is astraight or branched chain alpha-olefin of 3 to 6 carbon atoms.

In a further embodiment the straight chain alpha-olefin is propylene.

It is well known that e.g. propylene can be used as a comonomer or as achain transfer agent (CTA), or both, whereby it can contribute to thetotal amount of the vinyl groups in the polyethylene, P. Herein, whencopolymerisable CTA, such as propylene, is used, the copolymerised CTAis not calculated to the comonomer content.

In an exemplified embodiment, the polyethylene is an unsaturated LDPEpolymer, for example, an unsaturated LDPE copolymer comprising at leastone comonomer which is a polyunsaturated comonomer (referred herein asLDPE copolymer).

Further, said polyunsaturated comonomer may be a diene, for example, (1)a diene which comprises at least 8 carbon atoms, the first carbon-carbondouble bond being terminal and the second carbon-carbon double bondbeing non-conjugated to the first one (group 1 dienes). Exemplifieddienes (1) may be selected from C₈ to C₁₄ non-conjugated dienes ormixtures thereof, for example, selected from 1,7-octadiene,1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene,7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene, or mixtures thereof. Ina further embodiment, the diene (1) is selected from 1,7-octadiene,1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, or any mixturethereof.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein the polyethylene is a copolymer of amonomer with at least one polyunsaturated comonomer, wherein thepolyunsaturated comonomer is a straight carbon chain with at least 8carbon atoms and at least 4 carbon atoms between the non-conjugateddouble bonds, of which at least one is terminal, for example, C₈ to C₁₄non-conjugated diene, e.g. selected from 1,7-octadiene, 1,9-decadiene,1,11-dodecadiene, 1,13-tetradecadiene, or mixtures thereof.

In a preferred embodiment the polyethylene is a copolymer of ethyleneand 1,7-octadiene.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein the polyethylene is anunsaturated LDPE homopolymer or copolymer produced in a continuous highpressure polymerisation process, e.g. a LDPE copolymer of ethylene withone or more polyunsaturated comonomer(s) and with zero, one or moreother comonomer(s).

In addition or as an alternative to the dienes (1) listed herein, thediene may also be selected from other types of polyunsaturated dienes(2), such as from one or more siloxane compounds having the followingformula (group (2) dienes):CH₂═CH—[SiR₁R₂—O]_(n)—SiR₁R₂—CH═CH₂,

-   -   wherein n=1 to 200, and    -   R₁ and R₂, which can be the same or different, are selected from        C₁ to    -   C₄ alkyl groups and/or C₁ to C₄ alkoxy groups.

Further, R₁ and/or R₂ may, for example, be methyl, methoxy or ethoxy.Furthermore, n may, for example, be 1 to 100, e.g., 1 to 50. As anexample, divinylsiloxanes, for example, α,ω-divinylsiloxane can bementioned.

Exemplified polyunsaturated comonomers for the polyethylene are thedienes from group (1) as defined herein. The polyethylene may, forexample, be a copolymer of ethylene with at least one diene selectedfrom 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene,1,13-tetradecadiene, or any mixture thereof, and optionally with one ormore other comonomer(s). It is also exemplified that said polyethyleneis the herein-mentioned unsaturated LDPE copolymer. It may comprisefurther comonomers, e.g. polar comonomer(s), alpha-olefin comonomer(s),non-polar comonomer(s) or any mixture thereof.

As a polar comonomer, compound(s) containing hydroxyl group(s), alkoxygroup(s), carbonyl group(s), carboxyl group(s), ether group(s) or estergroup(s), or a mixture thereof can used.

Further, a non-polar comonomer, is/are compound(s) not containinghydroxyl group(s), alkoxy group(s), carbonyl group(s), carboxylgroup(s), ether group(s) nor ester group(s).

In a further embodiment, compounds containing carboxyl and/or estergroup(s) are used and, e.g., the compound is selected from the groups ofacrylate(s), methacrylate(s) or acetate(s), or any mixtures thereof.

If present in said unsaturated LDPE copolymer, the polar comonomer may,for example, be selected from the group of alkyl acrylates, alkylmethacrylates or vinyl acetate, or a mixture thereof. Further, saidpolar comonomers may, for example, be selected from C₁- to C₆-alkylacrylates, C₁- to C₆-alkyl methacrylates or vinyl acetate. Stillfurther, said polar copolymer comprises a copolymer of ethylene with C₁-to C₄-alkyl acrylate, such as methyl, ethyl, propyl or butyl acrylate,or vinyl acetate, or any mixture thereof.

The polyethylene, of the herein described polymer composition, can beprepared using i.a. any conventional polymerisation process andequipment, the conventional means as described herein for providingunsaturation and any conventional means for adjusting the MFR₂, in orderto control and adjust the process conditions to achieve a desiredbalance between MFR₂ and amount of vinyl groups of the polymerisedpolymer. The unsaturated LDPE polymer as defined herein, e.g. theunsaturated LDPE copolymer, of the polymer composition is produced incontinuous high pressure reactor by free radical initiatedpolymerisation (referred to as high pressure radical polymerisation).The usable high pressure (HP) polymerisation and the adjustment ofprocess conditions are well known and described in the literature, andcan readily be used by a skilled person to provide the herein describedinventive balance. Continuous high pressure polymerisation can beperformed in a tubular reactor or an autoclave reactor, e.g. in atubular reactor. One embodiment of continuous HP process is describedherein for polymerising ethylene optionally together with one or morecomonomer(s), for example, at least with one or more polyunsaturatedcomonomer(s), in a tubular reactor to obtain a LDPE homopolymer orcopolymer as defined herein. The process can be adapted to otherpolymers as well.

Further, the polyethylene, of the herein described polymer composition,may be produced in a high pressure reactor by free radicalpolymerisation (referred to as high pressure radical polymerisation).Free radical initiated polymerisation is very rapid and thus well suitedfor a continuous process where careful control of process parameters canbe obtained by continuous monitoring and adjustments. To the highpressure radical polymerisation process there is a continuous feed ofethylene and initiator. The high pressure radical polymerisation processis preferably an autoclave or tubular process, more preferably a tubularreactor. A high pressure tubular process typically produces apolyethylene with a more narrow molecular weight distribution and with alower degree of long chain branches and with another branching structurecompared to a polyethylene produced in an autoclave process if similarprocess conditions are used such as similar temperature profile, similarpressure and similar initiator feed. Typically, a tubular reactor alsohas more favourable production economics because they have higherethylene conversion rates.

In a further embodiment the polyethylene of the polymer composition ofthe layer(s) being comprised in the cable of the present invention, isproduced in a continuous high pressure tubular reactor.

Compression:

Ethylene is fed to a compressor mainly to enable handling of highamounts of ethylene at controlled pressure and temperature. Thecompressors are usually a piston compressor or diaphragm compressors.The compressor is usually a series of compressors that can work inseries or in parallel. Most common is 2-5 compression steps. Recycledethylene and comonomers can be added at feasible points depending on thepressure. Temperature is typically low, usually in the range of lessthan 200° C. or less than 100° C. Said temperature may, for example, beless than 200° C.

Tubular Reactor:

The mixture is fed to the tubular reactor. First part of the tube is toadjust the temperature of the fed ethylene; usual temperature is150-170° C. Then the radical initiator is added. As the radicalinitiator, any compound or a mixture thereof that decomposes to radicalsat an elevated temperature can be used. Usable radical initiators arecommercially available. The polymerisation reaction is exothermic. Therecan be several radical initiator injections points, e.g. 1-5 points,usually provided with separate injection pumps. Also ethylene andoptional comonomer(s) can be added at any time during the process, atany zone of the tubular reactor and/or from one or more injectionpoints, as well known. The reactor is continuously cooled e.g. by wateror steam. The highest temperature is called peak temperature and thelowest temperature is called radical initiator temperature. The “lowesttemperature” means herein the reaction starting temperature which iscalled the initiation temperature which is “lower” as evident to askilled person.

Suitable temperatures range from 80 to 350° C. and pressure from 100 to400 MPa. Pressure can be measured at least in the compression stage andafter the tube. Temperature can be measured at several points during allsteps. High temperature and high pressure generally increase output.Using various temperature profiles selected by a person skilled in theart will allow control of structure of polymer chain, i.e. Long ChainBranching and/or Short Chain branching, density, MFR, viscosity,Molecular Weight Distribution etc.

The reactor ends conventionally with a valve. The valve regulatesreactor pressure and depressurizes the reaction mixture from reactionpressure to separation pressure.

Separation:

The pressure is typically reduced to approx. 10 to 45 MPa, for exampleto approx. 30 to 45 MPa. The polymer is separated from the unreactedproducts, for instance gaseous products, such as monomer or the optionalcomonomer(s), and most of the unreacted products are recovered. Normallylow molecular compounds, i.e. wax, are removed from the gas. Thepressure can further be lowered to recover and recycle the unusedgaseous products, such as ethylene. The gas is usually cooled andcleaned before recycling.

Then the obtained polymer melt is normally mixed and pelletized.Optionally, or in some embodiments, additives can be added in the mixer.Further details of the production of ethylene (co)polymers by highpressure radical polymerisation can be found in the Encyclopedia ofPolymer Science and Engineering, Vol. 6 (1986), pp 383-410.

The MFR₂ of the polyethylene, e.g. LDPE copolymer, can be adjusted byusing e.g. chain transfer agent during the polymerisation, and/or byadjusting reaction temperature or pressure.

When the LDPE copolymer of the invention is prepared, then, as wellknown, the amount of vinyl groups can be adjusted by polymerising theethylene e.g. in the presence of one or more polyunsaturatedcomonomer(s), chain transfer agent(s), or both, using the desired feedratio between C₂ and polyunsaturated comonomer and/or chain transferagent, depending on the nature and amount of carbon carbon double bondsdesired for the LDPE copolymer. I.a. WO 9308222 describes a highpressure radical polymerisation of ethylene with polyunsaturatedmonomers, such as an α,ω-alkadienes, to increase the unsaturation of anethylene copolymer. The non-reacted double bond(s) thus provides pendantvinyl groups to the formed polymer chain at the site, where thepolyunsaturated comonomer was incorporated by polymerisation. As aresult the unsaturation can be uniformly distributed along the polymerchain in random copolymerisation manner. Also e.g. WO 9635732 describeshigh pressure radical polymerisation of ethylene and a certain type ofpolyunsaturated α,ω-divinylsiloxanes. Moreover, as known, e.g. propylenecan be used as a chain transfer agent to provide double bonds, wherebyit can also partly be copolymerised with ethylene.

The alternative unsaturated LDPE homopolymer may be produced analogouslyto the herein described process conditions as the unsaturated LDPEcopolymer, except that ethylene is polymerised in the presence of achain transfer agent only.

One exemplified polyethylene, e.g. of the LDPE copolymer, of the presentinvention may have a density, when measured on the polyethyleneaccording to ISO 1183-1 method A: 2012, of e.g. higher than 0.860 g/cm³,higher than 0.870, higher than 0.880, higher than 0.885, higher than0.890, higher than 0.895, higher than 0.900, higher than 0.905, higherthan 0.910, or of higher than 0.915 g/cm³.

Another exemplified polyethylene, e.g. of the LDPE copolymer, of thepresent invention may have a density, when measured on the polyethyleneaccording to ISO 1183-1 method A: 2012, of up to 0.960 g/cm³, less than0.955, less than 0.950, less than 0.945, less than 0.940, less than0.935, or of less than 0.930 g/cm³.

In a further embodiment the density range, when measured on thepolyethylene according to ISO 1183-1 method A: 2012, is from 0.915 to0.930 g/cm³.

Further, said unsaturated copolymer, e.g. the LDPE copolymer, of thepolymer composition comprises comonomer(s) in a total amount of up to 45wt %, e.g. of from 0.05 to 25 wt %, or e.g. from 0.1 to 15 wt %, basedon the amount of the polyethylene.

An exemplified polyethylene of the polymer composition is crosslinkable.

In an exemplified embodiment the polymer composition consists of the atleast one polyethylene. The polymer composition may comprise furthercomponents such as herein described additives which may be added in amixture with a carrier polymer, i.e. in so called master batch.

In a further embodiment, the polymer composition may comprise thepolyethylene, as described herein, together with the crosslinking agentand together with 0, 1, 2, 3, 4, 5, 6 or more additive(s), and whereinthe polymer composition is in the form of pellets.

A further embodiment of the present invention discloses a process forproducing a cable as described herein.

An embodiment of the present invention provides a cable, which is apower cable.

Further, the invention is highly suitable for W&C applications, wherebya cable, which is crosslinkable or crosslinked, comprises one or morelayers, wherein at least one layer is obtained from the polymercomposition as described herein.

Furthermore, still a further embodiment of the present invention isprovided, wherein the expression “is obtained from the polymercomposition” also comprises the feature “comprises the polymercomposition”.

A further embodiment of the present invention provides a power cablecomprising layer(s), e.g. insulating layer(s), which is/are obtainedfrom the polymer composition as described herein.

Still a further embodiment of the present invention is provided, whereinsaid cable is an AC power cable.

A further embodiment of the present invention is provided wherein saidcable is a DC power cable.

Still a further embodiment of the present invention is provided, whereinat least one layer of the cable obtained from the polymer compositionmay, e.g., be an insulation layer.

A further embodiment of the present invention is provided wherein atleast one layer of the cable comprising the polymer composition may,e.g., be an insulation layer.

Further, the cable of the present invention may, for example, be a powercable which comprises at least an inner semiconducting layer, aninsulation layer and an outer semiconducting layer in given order,wherein at least the insulation layer is obtained from the polymercomposition as described herein.

In a further embodiment, the insulation layer comprises the polymercomposition as described herein.

The power cable means herein a cable that transfers energy operating atany voltage. The voltage applied to the power cable can be AC, DC ortransient (impulse). In an embodiment, the power cable is operating atvoltages higher than 6 kV.

A further embodiment of the present invention discloses a process forproducing a cable, as described herein, which process comprises use of apolymer composition, as described herein.

Moreover, the invention provides a process for producing the hereindescribed cable, which comprises the steps of a) forming an article,wherein the process comprises the polymer composition as describedherein. Said process may, for example, comprise at least the steps of

a₀) meltmixing a polymer composition as described herein optionallytogether with further component(s), and

a) forming a cable obtained from the polymer composition as describedherein.

A further embodiment discloses forming a cable comprising the polymercomposition as described herein.

“Meltmixing” is well known blending method, wherein the polymercomponent(s) are mixed in an elevated temperature, which is typicallyabove, e.g. at least 20-25° C. above, the melting or softening point ofpolymer component(s).

In an embodiment a cable, which comprises a conductor surrounded by oneor more layers, is produced, wherein the process comprises a step of a)applying on a conductor the polymer composition, as described herein, toform at least one of said layers surrounding the conductor.

Thus in step (a) the at least one layer of said one or more layers isapplied and obtained by using the polymer composition as describedherein.

Also the herein exemplified cable production process may, for example,comprise at least two steps of

a₀) meltmixing said polymer composition, as described herein, optionallytogether with further component(s), and then

a) applying the meltmix obtained from step a₀) on a conductor to form atleast one layer.

The polymer composition, as described herein, may be introduced to stepa₀) of the process, e.g. in pellet form and mixing, i.e. meltmixing, iscarried out in an elevated temperature which melts (or softens) thepolymer material to enable processing thereof.

Further, layers of the cable may, for example, be a) applied by(co)extrusion. The term “(co)extrusion” means herein that in case of twoor more layers, said layers can be extruded in separate steps, or atleast two or all of said layers can be coextruded in a same extrusionstep, as well known in the art.

In one exemplified embodiment the crosslinkable polymer composition maycomprise a crosslinking agent before the polymer composition is used forcable production, whereby the polyethylene and the crosslinking agentcan be blended by any conventional mixing process, e.g. by addition ofthe crosslinking agent to a melt of a composition of polymer, e.g. in anextruder, as well as by adsorption of liquid peroxide, peroxide inliquid form or peroxide dissolved in a solvent on a solid composition ofpolymer, e.g. pellets thereof. Alternatively in this embodiment, thepolyethylene and the crosslinking agent can be blended by anyconventional mixing process. Exemplary mixing procedures include meltmixing, e.g. in an extruder, as well as adsorption of liquid peroxide,peroxide in liquid form or a peroxide dissolved in a solvent of acomposition of the polymer or on pellets thereof. The obtained polymercomposition of components, for example, a.o. the polyethylene and thecrosslinking agent, is then used for an article, e.g. a cable,preparation process.

In another embodiment, the crosslinking agent may be added e.g. in stepa₀) during the preparation of the crosslinkable article, and also formsthe polymer composition. When the crosslinking agent is added during thearticle preparation process, then, for example, the crosslinking agent,as described herein, is added in a liquid form at ambient temperature,or is preheated above the melting point thereof or dissolved in acarrier medium, as well known in the art.

The polymer composition may also comprise further additive(s), orfurther additive(s) may be blended to the polymer composition during apreparation process of an article comprising the polymer composition.

Accordingly the process of the invention may, for example, comprise thesteps of

a₀₀) providing to said step a₀) said polymer composition as describedherein, which comprises

-   -   at least one polyethylene, and    -   a crosslinking agent,

a₀) meltmixing the polymer composition optionally together with furthercomponents, and

a) applying the meltmix obtained from step a₀) on a conductor to form atleast one of said one or more cable layers.

Alternatively, the process of the invention comprises the steps of

a_(00′)) providing to said step a₀) said polymer composition asdescribed herein, which comprises

-   -   at least one polyethylene,

a₀′) adding to said polymer composition at least one crosslinking agent,

a₀) meltmixing the polymer composition and the crosslinking agent,optionally together with further components, and

a) applying the meltmix obtained from step a₀) on a conductor to form atleast one of said one or more cable layers.

In the exemplified process, the a₀) meltmixing of the polymercomposition alone is performed in a mixer or an extruder, or in anycombination thereof, at elevated temperature and, if crosslinking agentis present, then also below the subsequently used crosslinkingtemperature. After a₀) meltmixing, e.g. in said extruder, the resultingmeltmixed layer material is then, for example, a) (co)extruded on aconductor in a manner very well known in the field. Mixers andextruders, such as single or twins screw extruders, which are usedconventionally for cable preparation are suitable for the process of theinvention.

The exemplified embodiment of the process provides the preparation of acrosslinkable cable, e.g. a crosslinkable power cable, wherein theprocess comprises a further step of b) crosslinking the at least onecable layer obtained from step a) comprising a crosslinkablepolyethylene of the polymer composition, wherein the crosslinking isperformed in the presence of a crosslinking agent, e.g. a peroxide.

It is understood and well known that also the other cable layers andmaterials thereof, if present, can be crosslinked at the same time, ifdesired.

Crosslinking can be performed at crosslinking conditions, typically bytreatment at increased temperature, e.g. at a temperature above 140° C.,e.g. above 150° C., such as within the range of 160 to 350° C.,depending on the used crosslinking agent as well known in the field.Typically the crosslinking temperature is at least 20° C. higher thanthe temperature used in meltmixing step a₀) and can be estimated by askilled person.

As a result a crosslinked cable is obtained comprising at least onecrosslinked layer of the polymer composition.

In a further embodiment, a polymer composition is disclosed, whereinsaid total amount of vinyl groups, B, originates from (beside vinylgroups originating from free radical initiated polymerisation):

i) polyunsaturated comonomer(s),

ii) chain transfer agent(s),

iii) unsaturated low molecular weight compound(s), e.g. crosslinkingbooster(s) and/or scorch retarder(s), or

iv) any mixture of (i) to (iii).

In general, “vinyl group” means herein CH₂═CH— moiety which can bepresent in any of i) to iv).

The i) polyunsaturated comonomers and ii) chain transfer agents aredescribed herein in relation to the polyethylene of the polymercomposition.

The iii) low molecular weight compound(s), if present, may be added intothe polymer composition.

Further, the iii) low molecular weight compound(s) can, for example, becrosslinking booster(s) which may also contribute to said total amountof vinyl groups, B, of the polymer composition. The crosslinkingbooster(s) may be e.g. compound(s) containing at least 2, unsaturatedgroups, such as an aliphatic or aromatic compound, an ester, an ether,or a ketone, which contains at least 2, unsaturated group(s), such as acyanurate, an isocyanurate, a phosphate, an ortho formate, an aliphaticor aromatic ether, or an allyl ester of benzene tricarboxylic acid.Examples of esters, ethers, amines and ketones are compounds selectedfrom general groups of diacrylates, triacrylates, tetraacrylates,triallylcyanurate, triallylisocyanurate,3,9-divinyl-2,4,8,10-tetra-oxaspiro[5,5]-undecane (DVS), triallyltrimellitate (TATM) orN,N,N′,N′,N″,N″-hexaallyl-1,3,5-triazine-2,4,6-triamine (HATATA), or anymixtures thereof. The crosslinking booster can be added in an amount ofless than 2.0 wt %, for example, less than 1.5 wt %, e.g. less than 1.0wt %, for example, less than 0.75 wt %, e.g. less than 0.5 wt %, and thelower limit thereof is, for example, at least 0.05 wt %, e.g., at least0.1 wt %, based on the weight of the polymer composition.

Furthermore, the iii) low molecular weight compound(s) can, for example,be scorch retarder(s) (SR) which may also contribute to said totalamount of vinyl groups, B, of the polymer composition.

The scorch retarders (SR) may, e.g., be, as already described herein,unsaturated dimers of aromatic alpha-methyl alkenyl monomers, such as2,4-di-phenyl-4-methyl-1-pentene, substituted or unsubstituteddiphenylethylene, quinone derivatives, hydroquinone derivatives,monofunctional vinyl containing esters and ethers, monocyclichydrocarbons having at least two or more double bonds, or mixturesthereof. For example, the scorch retarder may be selected from2,4-diphenyl-4-methyl-1-pentene, substituted or unsubstituteddiphenylethylene, or mixtures thereof.

The amount of scorch retarder may, for example, be equal to, or morethan, 0.005 wt %, based on the weight of the polymer composition.Further, the amount of scorch retarder may, for example, be equal to, ormore than, 0.01 wt %, equal to, or more than, 0.03 wt %, or equal to, ormore than, 0.04 wt %, based on the weight of the polymer composition.

Still further, the amount of scorch retarder may, for example, be equalto, or less than, 0.35 wt %, e.g., equal to, or less than, 0.30 wt %,based on the weight of the polymer composition. Further, the amount ofscorch retarder may, for example, be equal to, or less than, 0.25 wt %,equal to, or less than, 0.20 wt %, equal to, or less than, 0.15 wt %, orequal to, or less than, 0.10 wt %, based on the weight of the polymercomposition. Moreover, the amount of scorch retarder may, for example,be equal to, or less than, 0.15 wt %, or equal to, or less than, 0.10 wt%, based on the weight of the polymer composition.

Further, the amount of scorch retarder may, for example, be equal to, orless than, 2.0 wt %, e.g., equal to, or less than, 1.5 wt %, based onthe weight of the polymer composition. Further, the amount of scorchretarder may, for example, be equal to, or less than, 0.8 wt %, equalto, or less than, 0.75 wt %, equal to, or less than, 0.70 wt %, or equalto, or less than, 0.60 wt %, based on the weight of the polymercomposition. Moreover, the amount of scorch retarder may, for example,be equal to, or less than, 0.55 wt %, equal to, or less than, 0.50 wt %,equal to, or less than, 0.45 wt %, or equal to, or less than, 0.40 wt %,based on the weight of the polymer composition.

Furthermore, the amount of scorch retarder may, for example, be withinthe range of 0.005 to 2.0 wt %, e.g., within the range of 0.005 to 1.5wt %, based on the weight of the polymer composition. Furtherexemplified ranges are e.g. from 0.01 to 0.8 wt %, 0.03 to 0.75 wt %,0.03 to 0.70 wt %, or 0.04 to 0.60 wt %, based on the weight of thepolymer composition. Moreover, exemplified ranges are e.g. from 0.01 to0.60, to 0.55, to 0.50, to 0.45 or, alternatively, to 0.40 wt %, 0.03 to0. 0.55 or, alternatively, to 0.50 wt %, 0.03 to 0.45 or, alternatively,0.40 wt %, or 0.04 to 0.45 or, alternatively, 0.40 wt %, based on theweight of the polymer composition.

Further, the scorch retarders (SR) may, e.g., also be selected fromgraftable stable organic free radicals, as described in EP1699882 and asalso already described herein.

The polyethylene of the polymer composition may, for example, be acopolymer of monomer units with units of at least one unsaturatedcomonomer(s) and zero, one, two or three other comonomer(s), andcomprises at least vinyl groups which originate from the polyunsaturatedcomonomer.

Further, the polyethylene of the polymer composition may comprise about0.05 to about 0.10 vinyl groups per 1000 carbon atoms (C-atoms) whichoriginate from the free radical initiated polymerisation.

In embodiments of the present invention the cable also comprises furtherlayer(s), which further layer(s) is/are obtained from semiconductingcomposition(s). The semiconducting composition(s) comprises a polymerpart, a conducting part and a crosslinking agent,

The polymer part may, e.g., comprise a polar polyethylene, e.g. alow-density polyethylene (LDPE) copolymer having at least a polarcomonomer.

The polar polyethylene contributes to better dispersion of theconducting part, e.g. carbon black, increasing adhesion and improvingprocessability. Further, the polar polyethylene has also a minor effectto improve space charge performance in a cable.

The amount of said polymer part of said semiconducting composition(s) ise.g. 41 to 75 wt %, for example 50 to 70 wt %.

The polymer part may optionally have an unsaturation that can preferablybe provided by copolymerising ethylene with at least one polyunsaturatedcomonomer as defined herein and/or by using a chain transfer agent, suchas propylene. Such polymer are well known and described e.g. in WO93/08222, EP 1695996 or WO2006/131266. Typically said unsaturatedpolyolefins have a double bond content of more than 0.1 doublebonds/1000 C-atoms.

According to an embodiment, the polymer part of said semiconductingcomposition(s) comprises a polar polyethylene being said LDPE copolymer,wherein the comonomer is selected from one or more of polar comonomer(s)and may optionally comprise an unsaturation provided preferably bycopolymerising ethylene with at least one polyunsaturated comonomer(s)and/or by using a chain transfer agent, such as propylene.

Still a further embodiment discloses a semiconducting composition,wherein said polymer part is a polar polyethylene copolymer, where acomonomer is selected from one or more of polar comonomer(s), and thepolar polyethylene copolymer may optionally comprise unsaturationprovided by, for example, copolymerising ethylene with at least onepolyunsaturated comonomer and/or by, for example, using a chain transferagent, e.g. propylene.

Further, said polyunsaturated comonomer may be a diene, for example, adiene which comprises at least 8 carbon atoms, the first carbon-carbondouble bond being terminal and the second carbon-carbon double bondbeing non-conjugated to the first one (group 1 dienes). Exemplifieddienes may be selected from C₈ to C₁₄ non-conjugated dienes or mixturesthereof, for example, selected from 1,7-octadiene, 1,9-decadiene,1,11-dodecadiene, 1,13-tetradecadiene, 7-methyl-1,6-octadiene,9-methyl-1,8-decadiene, or mixtures thereof. In a further embodiment,the diene is selected from 1,7-octadiene, 1,9-decadiene,1,11-dodecadiene, 1,13-tetradecadiene, or any mixture thereof.

Further, said polar comonomer(s) in said LDPE copolymer of ethylene withat least polar comonomer(s) of the polar polyethylene is/are selectedfrom: vinyl carboxylate esters, such as vinyl acetate and vinylpivalate, (meth)acrylates, such as methyl(meth)acrylate,ethyl(meth)acrylate, butyl(meth)acrylate and hydroxyethyl(meth)acrylate,olefinically unsaturated carboxylic acids, such as (meth)acrylic acid,maleic acid and fumaric acid, (meth)acrylic acid derivatives, such as(meth)acrylonitrile and (meth)acrylic amide, and vinyl ethers, such asvinyl methyl ether and vinyl phenyl ether.

The term “(meth)acrylic acid” and “(meth)acrylate” are intended toembrace both acrylic acid and methacrylic acid and, respectively“methacrylate” and “acrylate”.

A further embodiment discloses a semiconducting composition, whereinsaid polymer part is a polar polyethylene copolymer where a comonomer isselected from one or more of polar comonomer(s) and is/are selectedfrom:

vinyl carboxylate esters, such as vinyl acetate and vinyl pivalate,(meth)acrylates, such as methyl(meth)acrylate, ethyl(meth)acrylate,butyl(meth)acrylate and hydroxyethyl(meth)acrylate, olefinicallyunsaturated carboxylic acids, such as (meth)acrylic acid, maleic acidand fumaric acid, (meth)acrylic acid derivatives, such as(meth)acrylonitrile and (meth)acrylic amide, vinyl ethers, such as vinylmethyl ether and vinyl phenyl ether.

Furthermore, said LDPE copolymer of ethylene with at least polarcomonomer(s) is a LDPE copolymer of ethylene with one or more of vinylesters of monocarboxylic acids having 1 to 4 carbon atoms, such as vinylacetate, or of (meth)acrylates of alcohols having 1 to 4 carbon atoms,or of a mixture thereof, e.g. of methyl (meth)acrylate, ethyl(meth)acrylate or butyl (meth)acrylate. An exemplified subgroup of saidLDPE copolymer of ethylene with at least polar comonomer(s) is a LDPEcopolymer of ethylene with at least vinyl acetate, LDPE copolymer ofethylene with at least methyl acrylate, a LDPE copolymer of ethylenewith at least ethyl acrylate or a LDPE copolymer of ethylene with atleast butyl acrylate, or any mixture thereof.

The content of polar comonomer in said LDPE copolymer of ethylene withat least polar comonomer(s) as defined herein, as said polymer part maybe, e.g., not limited and may, for example, be of up to 70 wt %, e.g. of0.5 to 35 wt %, for example, of 1.0 to 35 wt %, of the total amount ofsaid LDPE copolymer.

An even further embodiment discloses a semiconducting composition,wherein said polymer part is a polar polyethylene copolymer being acopolymer of ethylene with one or more of vinyl esters of monocarboxylicacids having 1 to 4 carbon atoms, e.g. vinyl acetate, or of(meth)acrylates of alcohols having 1 to 4 carbon atoms, or of a mixturethereof, for example, of methyl (meth)acrylate, ethyl (meth)acrylate orbutyl (meth)acrylate, wherein an exemplified subgroup of said polarpolyethylene copolymer of ethylene with at least polar comonomer(s) is apolar polyethylene copolymer of ethylene with at least vinyl acetate,polar polyethylene copolymer of ethylene with at least methyl acrylate,a polar polyethylene copolymer of ethylene with at least ethyl acrylateor a polar polyethylene copolymer of ethylene with at least butylacrylate, or any mixture thereof.

The amount of polar group containing comonomer units in the polarpolyethylene is from 5 to 40 wt %, in suitably from 10 to 30 wt %, andyet more suitably from 10 to 25 wt %.

In a suitable embodiment, the total amount of polar comonomers in thepolar polyethylene is from 1 wt % to 20 wt %, suitably 5 wt % to 20 wt%.

A further embodiment discloses a semiconducting composition, wherein thecontent of polar comonomer in said polar polyethylene copolymer ofethylene with at least polar comonomer(s) e.g. as said polymer part isnot limited and may be of up to 70 wt %, for example, 0.5 to 35 wt %,e.g. 1.0 to 35 wt %, of the total amount of said polar polyethylenecopolymer.

Further, the content of polar comonomer in said polar polyethylenecopolymer of ethylene with at least polar comonomer(s) may in furtherembodiments be of up to 60 wt %, up to 55 wt %, up to 50 wt %, up to 45wt %, or up to 40 wt %.

Still further embodiments disclose a semiconducting composition, whereinthe content of polar comonomer in said polar polyethylene copolymer ofethylene with at least polar comonomer(s) may be, for example, 0.5 to 40wt %, e.g. 1.0 to 40 wt %, for example, 2 to 40 wt %, e.g. 3 to 40 wt %,for example, 4 to 40 wt %, e.g. 5 to 40 wt %, for example, 2 to 35 wt %,e.g. 3 to 35 wt %, for example, 4 to 35 wt %, e.g. 5 to 35 wt %, forexample, 0.5 to 30 wt %, e.g. 1.0 to 30 wt %, for example, 2 to 30 wt %,e.g. 3 to 30 wt %, or for example, 4 to 30 wt %, e.g. 5 to 30 wt %, ofthe total amount of said polar polyethylene copolymer.

Suitable LDPE copolymer of ethylene with at least polar comonomer(s) iscopolymer of ethylene and:

vinyl esters of monocarboxylic acids having 1 to 4 carbon atoms, such asvinyl acetate (EVA),

(meth)acrylates of alcohols having 1 to 4 carbon atoms, such as methyl(meth)acrylate (EMA & EMMA),

butyl acrylate (EBA),

ethyl acrylate (EEA) and

methyl acrylate (EMA).

Further, especially suitable comonomers are butyl acrylate, ethylacrylate and methyl acrylate.

In even a further embodiment, said polymer part of said semiconductingcomposition may be a polymer of an alpha-olefin which includes ahomopolymer of ethylene or copolymer of ethylene with one or morecomonomers, which is selected from a branched polyethylene homo- orcopolymer produced at high pressure by free radical initiatedpolymerisation (referred to as high pressure radical polymerization) andwell known as low density polyethylene (LDPE) copolymer, which isreferred herein as LDPE copolymer, or a linear polyethylene homo- orcopolymer produced by low pressure polymerisation using a coordinationcatalyst, such as well known linear very low density polyethylene(VLDPE), linear low density polyethylene (LLDPE), medium densitypolyethylene (MDPE) or high density polyethylene (HDPE), which isreferred herein as “linear PE homo- or copolymer”, or a mixture of suchpolymers.

The polymer part of said semiconducting composition may comprise saidlinear PE copolymer, which is, for example, VLDPE, LLDPE, MDPE or HDPEpolymer. They can be produced in a known manner in a single ormultistage processes e.g. as slurry polymerisation, a solutionpolymerisation, a gas phase polymerisation, and in case of multistageprocess in any combination(s) thereof, in any order, using one or moreof e.g. Ziegler-Natta catalysts, single site catalysts, includingmetallocenes and non-metallocenes, and Cr-catalysts. The preparation oflinear ethylene polymer is and the used catalysts are very well known inthe field, and as an example only, reference is made i.a. to amultistage process described in EP517868.

Continuous high pressure polymerisation for producing said LDPE homo orcopolymer and the subgroups as defined herein, is a well knowntechnology in the polymer field and can be affected in a tubular or anautoclave reactor, for example, in a tubular reactor. The continuoushigh pressure polymerisation is carried out suitably in a known manner,e.g. at temperature range from 80 to 350° C. and pressure of from 100 to400 MPa typically in the presence of an initiator of the freeradical/polymerisation reaction. Further details about high pressureradical polymerisation are given in WO 93/08222. The polymerisation ofthe high pressure process is generally performed at pressures of from1200 to 3500 bar and temperatures of from 150 to 350° C.

MFR₂₁, of said semiconducting composition(s) may typically be at least1.0 g/10 min, suitably at least 3.0 g/10 min, for example, at least 5.0g/10 min, e.g. at least 6.0 g/10 min, for example, at least 8.0 g/10min, when measured according to ISO1133, 21.6 kg load, 190° C. MFR₂₁ ismeasured on said semiconducting composition(s) in absence ofcrosslinking agent. The upper limit MFR₂₁ of said semiconductingcomposition(s) is not limited and may be e.g. up 100 g/10 min, such asup to 80 g/10 min, for example, up to 60 g/10 min, e.g. up to 50 g/10min, when determined as defined herein.

According to an embodiment said semiconducting composition(s) is in theform of pellets. The term pellets include herein granules and pellets ofany shape and type and are very well known and can be produced in knownmanner using the conventional pelletising equipment.

Said semiconducting composition(s) may comprise further components,typically additives, such as antioxidants, crosslinking boosters, scorchretardants, processing aids, fillers, coupling agents, ultravioletabsorbers, stabilizers, antistatic agents, nucleating agents, slipagents, plasticizers, lubricants, viscosity control agents, tackifiers,anti-blocking agents, surfactants, extender oils, acid scavengers and/ormetal deactivators.

Examples of such antioxidants are as follows, but are not limited to:hindered phenols such astetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydro-cinnamate)] methane;bis[(beta-(3,5-ditert-butyl-4-hydroxybenzyl)-methylcarboxyethyl)]sulphide,4,4′-thiobis(2-methyl-6-tert-butylphenol),4,4′-thiobis(2-tert-butyl-5-methylphenol),2,2′-thiobis(4-methyl-6-tert-butylphenol), and thiodiethylenebis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate; phosphites andphosphonites such as tris(2,4-di-tert-butylphenyl)phosphite anddi-tert-butylphenyl-phosphonite; thio compounds such asdilaurylthiodipropionate, dimyristylthiodipropionate, anddistearylthiodipropionate; various siloxanes; polymerized2,2,4-trimethyl-1,2-dihydroquinoline,n,n′-bis(1,4-dimethylpentyl-p-phenylenediamine), alkylateddiphenylamines, 4,4′-bis(alpha,alpha-demthylbenzyl)diphenylamine,diphenyl-p-phenylenediamine, mixed di-aryl-p-phenylenediamines,2,2′-oxamidobis-(ethyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)propionate), and otherhindered amine antidegradants or stabilizers. Antioxidants can be usedin amounts of about 0.1 to about 5 percent by weight based on the weightof the composition.

The semiconducting composition(s) may comprise further components, e.g.additives and/or further polymer parts. Examples of further fillers asadditives are as follows: clays, precipitated silica and silicates,fumed silica, calcium carbonate, ground minerals, and further carbonblacks. Fillers can be used in amounts ranging from less than about 0.01to more than about 50 percent by weight based on the weight of thecomposition.

In further embodiments, the semiconducting composition(s), may comprise35 to 90 wt % of the polymer part, for example, the polar polyethylene,10 to 60 wt % of a conducting part comprising carbon black and 0 to 8 wt% additives, wherein all wt % are based on the total of eachsemiconducting composition.

The semiconductive properties of the semiconducting composition(s)result from the conducting part comprised in each semiconductingcomposition. The conducting part is comprised in each semiconductingcomposition in, at least, an amount that renders each semiconductingcomposition semiconducting. Further, the conducting part is suitably acarbon black.

Depending on the desired use, the conductivity of the carbon black andconductivity of the composition, the amount of carbon black can vary.The semiconducting composition(s) comprises, for example, 10 to 60 wt %,e.g. 10 to 50 wt %, carbon black, based on the weight of eachsemiconducting composition. In other embodiments, the lower limit of theamount of carbon black is 10 wt %, e.g. 20 wt % or, for example 25 wt %,based on the weight of each semiconducting composition. The upper limitof the amount of carbon black is, for example 50 wt %, e.g. 45 wt % or,for example 41 wt %, based on the weight of each semiconductingcomposition.

Still a further embodiment discloses a semiconducting composition,wherein the amount of the carbon black is 10 to 60 wt %, e.g. 10 to 50wt %, for example, 20 to 45, e.g. 30 to 40 wt %, for example, 35 to 40wt %.

Any carbon black which is electrically conductive can be used. Further,the carbon black may have a nitrogen surface area (BET) of 5 to 400m²/g, for example of 10 to 300 m²/g, e.g. of 30 to 200 m²/g, whendetermined according to ASTM D3037-93. Further, the carbon black mayhave one or more of the following properties: i) a primary particle sizeof at least 5 nm which is defined as the number average particlediameter according to ASTM D3849-95a procedure D, ii) iodine adsorptionnumber (IAN) of at least 10 mg/g, for example 10 to 300 mg/g, e.g. 30 to200 mg/g, when determined according to ASTM D-1510-07; and/or iii) DBP(dibutyl phthalate) absorption number (=oil number) of at least 30cm³/100 g, for example 60 to 300 cm³/100 g, e.g. 70 to 250 cm³/100 g,for example 80 to 200 cm³/100 g, e.g. 90 to 180 cm³/100 g, when measuredaccording to ASTM D 2414-06a.

Furthermore, the carbon black may have one or more of the followingproperties: a) a primary particle size of at least 5 nm which is definedas the number average particle diameter according ASTM D3849-95a, b)iodine number of at least 30 mg/g according to ASTM D1510, c) oilabsorption number of at least 30 ml/100 g which is measured according toASTM D2414. Non-limiting examples of suitable carbon blacks includefurnace blacks and acetylene blacks. One group of suitable furnaceblacks have a primary particle size of 28 nm or less. The mean primaryparticle size is defined as the number average particle diametermeasured according to ASTM D3849-95a. Particularly suitable furnaceblacks of this category may have an iodine number between 60 and 300mg/g according to ASTM D1510. It is further suitable that the oilabsorption number (of this category) is between 50 and 225 ml/100 g, forexample between 50 and 200 ml/100 g and this is measured according toASTM D2414.

Another group of equally suitable furnace blacks have a primary particlesize of greater than 28 nm. The mean primary particle size is defined asthe number average particle diameter according to ASTM D3849-95a.Suitable furnace blacks of this category have an iodine number between30 and 200 mg/g according to ASTM D1510. Further the oil absorptionnumber (of this category) is, for example, between 80 and 300 ml/100 gmeasured according to ASTM D2414.

Other suitable carbon blacks can be made by any other process or can befurther treated.

Suitable carbon blacks for semiconducting cable layers are suitablycharacterized by their cleanliness. Therefore, suitable carbon blackshave an ash-content of less than 0.2 wt % measured according to ASTMD1506, a 325 mesh sieve residue of less than 30 ppm according to ASTMD1514 and have less than 1 wt % total sulphur according to ASTM D1619.

Furnace carbon black is generally acknowledged term for the well knowncarbon black type that is produced in a furnace-type reactor. Asexamples of carbon blacks, the preparation process thereof and thereactors, reference can be made to i.a. EP629222 of Cabot, U.S. Pat.Nos. 4,391,789, 3,922,335 and 3,401,020. As an example of commercialfurnace carbon black grades described in ASTM D 1765-98b i.a. N351, N293and N550, can be mentioned. Furnace carbon blacks are conventionallydistinguished from acetylene carbon blacks which are another carbonblack type suitable for the semiconducting composition(s), Acetylenecarbon blacks are produced in an acetylene black process by reaction ofacetylene and unsaturated hydrocarbons, e.g. as described in U.S. Pat.No. 4,340,577.

Particularly, acetylene blacks may have a particle size of larger than20 nm, for example 20 to 80 nm. The mean primary particle size isdefined as the number average particle diameter according to the ASTMD3849-95a. Suitable acetylene blacks of this category have an iodinenumber between 30 to 300 mg/g, for example 30 to 150 mg/g according toASTM D1510. Further the oil absorption number (of this category) is, forexample between 80 to 300 ml/100 g, e.g. 100 to 280 ml/100 g and this ismeasured according to ASTM D2414. Acetylene black is a generallyacknowledged term and are very well known and e.g. supplied by Denka.

A further embodiment discloses a semiconducting composition, wherein theconducting part is comprising, or is selected from, a conductive carbonblack, e.g. a carbon black with one or more, for example, all, of thefollowing properties: a primary particle size of at least 5 nm which isdefined as the number average particle diameter according to ASTMD3849-95a procedure D; an iodine adsorption number (IAN) of at least 10mg/g, e.g., 10 to 300 mg/g, when determined according to ASTM D-1510-07;or a DBP (dibutyl phthalate) absorption number (=oil number) of at least30 cm³/100 g, e.g. 60 to 300 cm³/100 g, when measured according to ASTMD 2414-06a.

The crosslinking agent comprised in said semiconducting composition(s)may be, separately and independently for each individual semiconductingcomposition, as defined as for any of the crosslinking agents comprisedin the polymer composition, as described herein.

In accordance with the present invention each feature in any of theherein disclosed embodiments, in any category of the present invention,may freely be combined with any feature in any of the other hereindisclosed embodiments.

Determination Methods

Unless otherwise stated in the description or experimental part thefollowing methods were used for the property determinations.

Melt Flow Rate

The melt flow rate (MFR) is determined according to method ISO1133-1:2011 and is indicated in g/10 min. The MFR is an indication ofthe flowability, and hence the processability, of the polymer, here thepolyethylene, or of the polymer composition. The higher the melt flowrate, the lower the viscosity of the polymer, or of the polymercomposition. The MFR is determined at 190° C. for polyethylenes and maybe determined at different loadings such as 2.16 kg (MFR₂) or 21.6 kg(MFR₂₁).

Density

Density is measured on the polymer, i.e. on the polyethylene, accordingto ISO 1183-1 method A: 2012. Sample preparation is done by compressionmoulding in accordance with ISO 17855-2:2016.

Methods ASTM D3124-98, and ASTM D6248-98, to Determine Amount of DoubleBonds in the Polymer Composition or in the Polymer, i.e. thePolyethylene

The method ASTM D6248-98 apply for determination of double bonds, both,in the polymer composition and in the polyethylene. Determination ofdouble bonds of the polymer composition is made either on thepolyethylene (to determine the parameter P) or, alternatively, on thepolymer composition (to determine the parameter B). The polymercomposition and the polyethylene are, hereinafter in this methoddescription, referred to as “the composition” and “the polymer”,respectively.

The methods ASTM D3124-98, and ASTM D6248-98, include on one hand aprocedure for the determination of the amount of double bonds/1000C-atoms which is based upon the ASTM D3124-98 method. In the ASTMD3124-98 method, a detailed description for the determination ofvinylidene groups/1000 C-atoms is given based on2,3-dimethyl-1,3-butadiene. In the ASTM D6248-98 method, detaileddescriptions for the determination of vinyl and trans-vinylenegroups/1000 C-atoms are given based on 1-octene and trans-3-hexene,respectively. The described sample preparation procedure therein hashere been applied for the determination of vinyl groups/1000 C-atoms andtrans-vinylene groups/1000 C-atoms in the present invention. The ASTMD6248-98 method suggests possible inclusion of the bromination procedureof the ASTM D3124-98 method but the samples with regard to the presentinvention were not brominated. We have demonstrated that thedetermination of vinyl groups/1000 C-atoms and trans-vinylenegroups/1000 C-atoms can be done without any significant interferenceseven without subtraction of spectra from brominated samples. For thedetermination of the extinction coefficient for these two types ofdouble bonds, the following two compounds have been used: 1-decene forvinyl and trans-4-decene for trans-vinylene, and the procedure asdescribed in ASTM-D6248-98 was followed with above the mentionedexception.

The total amount of vinyl bonds, vinylidene bonds and trans-vinylenedouble bonds of “the polymer” was analysed by means of IR spectrometryand given as the amount of vinyl bonds, vinylidene bonds andtrans-vinylene bonds per 1000 carbon atoms.

Further, the total amount of vinyl and trans-vinylene double bonds of“the composition”, with a possible contribution of double bonds from anyused unsaturated low molecular weight compound (iii), may also beanalysed by means of IR spectrometry and given as the amount of vinylbonds, vinylidene bonds and trans-vinylene bonds per 1000 carbon atoms.

The composition or polymer to be analysed were pressed to thin filmswith a thickness of 0.5-1.0 mm. The actual thickness was measured. FT-IRanalysis was performed on a Perkin Elmer Spectrum One. Two scans wererecorded with a resolution of 4 cm⁻¹.

A base line was drawn from 980 cm⁻¹ to around 840 cm⁻¹. The peak heightswere determined at around 910 cm⁻¹ for vinyl and around 965 cm⁻¹ fortrans-vinylene. The amount of double bonds/1000 carbon atoms wascalculated using the following formulae:vinyl/1000 C-atoms=(14×Abs)/(13.13×L×D)trans-vinylene/1000 C-atoms=(14×Abs)/(15.14×L×D)

-   -   wherein    -   Abs: absorbance (peak height)    -   L: film thickness in mm    -   D: density of the material (g/cm³)

The molar absorptivity, ε, i.e. 13.13 and, 15.14, respectively, in theabove calculations was determined as 1·mol⁻¹·mm⁻¹ via:ε=Abs/(C×L)

where Abs is the maximum absorbance defined as peak height, C theconcentration (mol·l⁻¹) and L the cell thickness (mm).

The methods ASTM D3124-98, and ASTM D6248-98, include on the other handalso a procedure to determine the molar extinction coefficient. At leastthree 0.18 mol·l⁻¹ solutions in carbon disulphide (CS₂) were used andthe mean value of the molar extinction coefficient used.

The amount of vinyl groups originating from the polyunsaturatedcomonomer per 1000 carbon atoms was determined and calculated asfollows:

The polymer to be analysed and a reference polymer have been produced onthe same reactor, basically using the same conditions, i.e. similar peaktemperatures, pressure and production rate, but with the only differencethat the polyunsaturated comonomer is added to the polymer to beanalysed and not added to reference polymer. The total amount of vinylgroups of each polymer was determined by FT-IR measurements, asdescribed herein. Then, it is assumed that the base level of vinylgroups, i.e. the ones formed by the process and from chain transferagents resulting in vinyl groups (if present), is the same for thereference polymer and the polymer to be analysed with the only exceptionthat in the polymer to be analysed also a polyunsaturated comonomer isadded to the reactor. This base level is then subtracted from themeasured amount of vinyl groups in the polymer to be analysed, therebyresulting in the amount of vinyl groups/1000 C-atoms, which result fromthe polyunsaturated comonomer.

The Methods ASTM D3124-98, and ASTM D6248-98, Include a CalibrationProcedure for Measuring the Double Bond Content of an Unsaturated LowMolecular Weight Compound (iii), if Present (Referred Below as Compound)

The molar absorptivity for Compound (e.g. a crosslinking booster or ascorch retarder compound as exemplified in the description) can bedetermined with said methods according to ASTM D6248-98. At least threesolutions of the Compound in CS₂ (carbon disulfide) are prepared. Theused concentrations of the solutions are close to 0.18 mol/l. Thesolutions are analysed with FTIR and scanned with resolution 4 cm⁻¹ in aliquid cell with path length 0.1 mm. The maximum intensity of theabsorbance peak that relates to the unsaturated moiety of theCompound(s) (each type of carbon-carbon double bonds present) ismeasured.

The molar absorptivity, ε, in l·mol⁻¹·mm⁻¹ for each solution and type ofdouble bond is calculated using the following equation:ε=(1/CL)×Abs

C=concentration of each type of carbon-carbon double bond to bemeasured, mol/l

L=cell thickness, mm

Abs=maximum absorbance (peak height) of the peak of each type ofcarbon-carbon double bond to be measured, mol/l.

The average of the molar absorptivity, ε, for each type of double bondis calculated. Further, the average molar absorptivity, ε, of each typeof carbon-carbon double bond can then be used for the calculation of theconcentration of double bonds in the reference polymer and the polymersamples to be analysed.

Rheology, Dynamic (Viscosity) Method ISO 6721-1

Dynamic rheological properties of the polymer, here the polyethylene, orof the polymer composition (also measured on the polyethylene) may bedetermined using a controlled stress rheometer, using a parallel-plategeometry (25 mm diameter) and a gap of 1.8 mm between upper and bottomplates. Previous to test, samples need to be stabilized by dry blendingpellets together with 0.25-0.3% Irganox B225. Irganox B 225 is a blendof 50% Irganox 1010, Pentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), CAS-no.6683-19-8 and 50% lrgafos 168, Tris(2,4-di-tert-butylphenyl) phosphite,CAS-no. 31570-04-4. Note that to add an antioxidant, here Irganox B225,is normally not the standard procedure of method ISO 6721-1.

Frequency sweep test, i.e. the “Rheology, dynamic (Viscosity) method”,was performed according to the ISO standard method, ISO 6721-1 with anangular frequency range from 500 to 0.02 rad/s. All experiments wereconducted under nitrogen atmosphere at a constant temperature of 190° C.and strain within the linear viscoelastic region. During analysis,storage modulus (G″), loss modulus (G″), complex modulus (G*) andcomplex viscosity (η*) were recorded and plotted versus frequency (ω).The measured values of complex viscosity (η*) at angular frequency of0.05, 100 and 300 rad/s are taken from test. The abbreviation of theseparameters are η_(0.05)*, η₁₀₀* and η₃₀₀* respectively.

The zero viscosity η*₀ value is calculated using Carreau-Yasuda model.For cases when the use of this model for the estimation of the Zeroshear viscosity is not recommendable a rotational shear test at lowshear rate is performed. This test is limited to a shear rate range of0.001 to 1 s⁻¹ and a temperature of 190° C.

Preparation of Cable, i.e. Cable Core, i.e. Cable of the PresentInvention and Comparative Cable

Polymer pellets of the test polymer compositions, i.e. polymercomposition comprised in the cable according to the present inventionand polymer composition comprised in the comparative cable were used toproduce 10 kV cables, i.e. cable cores, i.e. cable of the presentinvention and comparative cable, on a Maillefer pilot cable line ofcatenary continuous vulcanizing (CCV) type. The polymer pellets comprisepolyethylene and a crosslinking agent, here peroxide. The producedcables have 3.4 mm nominal insulation thickness obtained from thepolymer composition or from comparative polymer composition, and aninner semiconducting layer, which is 1.0 mm thick, and an outersemiconducting layer which is 1.0 mm thick. The conductors of the cablecores have a cross section being 50 mm² of stranded aluminium. Thecables, i.e. cable cores, were produced by extrusion via a triple head.The curing tube is composed of 4 zones (Z1, Z2, Z3 and Z4) and thetemperature used in each zone for the cable extrusion were as follow:Z1=490° C., Z2=415° C., Z3=396° C. and Z4=376° C. The semiconductingmaterial used as the inner and outer semiconducting material was LE0592(a commercially semiconducting material supplied by Borealis). The cablecores were produced with a line speed of 5.76 m/min when the polymerpellets of the insulation layer contained tert-butylcumyl-peroxide(TBCP) as peroxide and with a line speed of 5.2 m/min when the polymerpellets of the insulation contained2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, i.e. Trigonox® 145-E85,(T145E85) as peroxide.

Gas Chromatography (GC)-Analysis Protocol, i.e. Method for GC-Analysis

GC-Analysis protocol of cable, (i.e. cable core, i.e. cable of thepresent invention and comparative cable), i.e. the method forGC-Analysis

The volatile peroxide decomposition products, herein methane (CH₄),content is given in ppm (weight) and is determined by gas chromatography(GC) on a sample taken from a cable core comprising crosslinkedlayer(s), i.e. from the cable according to the present invention andfrom the comparative cable. The sample is taken from a layer material ofa cable sample from a crosslinked and cooled cable at the exit of acrosslinking/cooling zone. The exit of the crosslinking/cooling zonemay, e.g., be at an exit of a vulcanisation tube, i.e. after apressurised cooling step performed in a manner that is known for askilled person.

A pie shaped sample specimen with a weight of 5 g is cut from the cablecore sample within 15 minutes after the cable exited thecrosslinking/cooling zone. The cable core sample comprises bothcrosslinked insulation and semiconducting layers. The obtained sample isplaced in a 620 ml head space bottle with an aluminium crimp cup withTeflon seal and heat treated at 120° C. for 3 hours to equilibrate anygaseous volatiles present in said sample. Then 0.2 ml of the gascaptured in the sample bottle is injected into the gas chromatograph,wherein the presence and content of the volatiles, e.g. methane, whichare desired to be measured is analysed. Double samples are analysed andthe reported methane content value is an average of both analyses. Theinstrument used herein was an Agilent GC 7890A with an Al₂O₃/Na₂SO₄—column with the dimensions 0.53 mm×50 m and a film thickness of 10 μm,supplied by Plot Ultimetal. Helium was used as carrier gas and FIDdetection was used.

Method for Hot Set Determination

Hot Set Method for sample from cable, i.e. cable core, i.e. cable of thepresent invention and comparative cable

The hot set elongation as well as the permanent deformation weredetermined on samples taken from the middle of the insulation layer ofthe cable core, i.e. layer(s) from the crosslinked cable according tothe present invention and also from a crosslinked comparative cable,prepared as described herein under “Preparation of cable core”. Theseproperties were determined according to IEC 60811-507:2012. In the hotset test, a dumbbell, i.e. a sample specimen, of the tested material isequipped with a weight corresponding to 20 N/cm². Firstly, all thesample specimens are marked with reference lines. From the middle ofeach sample specimen, two reference lines (one on each side) are made.The distance between the two lines, L0 is 20 mm. The sample specimen isput into an oven at 200° C. with the weight correponding to 20 N/cm² andafter 15 minutes, the hot set elongation is measured as follow. Thedistance between references line after 15 min at 200° C. is called L1and is measured. Then the elongation after 15 min is calculated asfollows: hot set elongation (%)=((L1*100)/L0)−100. Subsequently, theweight is removed and the sample specimen is allowed to relax for 5minutes at 200° C. Then, the sample specimen is taken out from the ovenand is cooled down to room temperature. After cooling, the distance L2between the 2 reference lines is measured and the permanent deformationis calculated as follow: permanent deformation (%)=(L2*100)/L0)−100. Thedumbbells, i.e. the sample specimens, are prepared from the middle ofthe insulation layer of the cable core according to IEC 60811-501:2012and have a thickness of 1 mm.

EXPERIMENTAL PART Examples The Polyethylene

The polyethylenes are all low density polyethylenes polymerised in acontinuous high pressure tubular reactor.

Inventive Example (Inv. Ex.) 1: (Inventive Polymer (Inv. pol.) 1: Poly(ethylene-co-1,7-octadiene) polymer with 0.89 vinyl groups/1000 carbonatoms (C), Density=923.7 kg/m³, MFR₂=0.92 g/10 min), i.e. polyethyleneof the polymer composition, from which polymer composition, thelayer(s), being comprised in the cable of the present invention, is/areobtained

Ethylene with recycled CTA was compressed in a 5-stage precompressor anda 2-stage hyper compressor with intermediate cooling to reach initialreaction pressure of ca 2800 bar. The total compressor throughput was ca30 tons/hour. In the compressor area approximately 3.8 kg/hour ofpropion aldehyde (PA, CAS number: 123-38-6) was added as chain transferagent to maintain an MFR₂ of 0.92 g/10 min. Here also 1,7-octadiene wasadded to the reactor in amount of 89 kg/h. The compressed mixture washeated to 162° C. in a preheating section of a front feed three-zonetubular reactor with an inner diameter of ca 40 mm and a total length of1200 meters. A mixture of commercially available peroxide radicalinitiators dissolved in isododecane was injected just after thepreheater in an amount sufficient for the exothermal polymerisationreaction to reach peak temperatures of ca 286° C. after which it wascooled to approximately 231° C. The subsequent 2^(nd) and 3^(rd) peakreaction temperatures were 274° C. and 248° C. respectively with acooling in between to 222° C. The reaction mixture was depressurised bya kick valve, cooled and the resulting polymer “Inv. pol. 1” wasseparated from unreacted gas.

Inv. Ex. 2: (Inv. pol. 2: Poly (ethylene-co-1,7-octadiene) polymer with1.33 vinyl groups/1000 C, Density=924.3 kg/m³, MFR₂=0.94 g/10 min), i.e.polyethylene of the polymer composition, from which polymer composition,the layer(s), being comprised in the cable of the present invention,is/are obtained

Ethylene with recycled CTA was compressed in a 5-stage precompressor anda 2-stage hyper compressor with intermediate cooling to reach initialreaction pressure of ca 2800 bar. The total compressor throughput was ca30 tons/hour. In the compressor area approximately 2.3 kg/hour ofpropion aldehyde (PA, CAS number: 123-38-6) was added as chain transferagent to maintain an MFR₂ of 0.94 g/10 min. Here also 1,7-octadiene wasadded to the reactor in amount of 144 kg/h. The compressed mixture washeated to 160° C. in a preheating section of a front feed three-zonetubular reactor with an inner diameter of ca 40 mm and a total length of1200 meters. A mixture of commercially available peroxide radicalinitiators dissolved in isododecane was injected just after thepreheater in an amount sufficient for the exothermal polymerisationreaction to reach peak temperatures of ca 274° C. after which it wascooled to approximately 207° C. The subsequent 2^(nd) and 3^(rd) peakreaction temperatures were 257° C. and 227° C. respectively with acooling in between to 211° C. The reaction mixture was depressurised bya kick valve, cooled and polymer “Inv. pol. 2” was separated fromunreacted gas.

Comparative example (Comp. Ex.) 1: (Comparative Polymer (Comp. pol.) 1:Poly (ethylene-co-1,7-octadiene) polymer with 0.71 vinyl groups/1000 C,Density=922.3 kg/m³, MFR₂=0.68 g/10 min), i.e. polyethylene ofcomparative polymer composition from which layer(s), comprised in acable, is/are obtained

Ethylene with recycled CTA was compressed in a 5-stage precompressor anda 2-stage hyper compressor with intermediate cooling to reach initialreaction pressure of ca 2900 bar. The total compressor throughput was ca30 tons/hour. In the compressor area approximately 1.2 kg/hour ofpropion aldehyde (PA, CAS number: 123-38-6) was added together withapproximately 87 kg propylene/hour as chain transfer agents to maintainan MFR₂ of 0.68 g/10 min. Here also 1,7-octadiene was added to thereactor in amount of 56 kg/h. The compressed mixture was heated to 164°C. in a preheating section of a front feed three-zone tubular reactorwith an inner diameter of ca 40 mm and a total length of 1200 meters. Amixture of commercially available peroxide radical initiators dissolvedin isododecane was injected just after the preheater in an amountsufficient for the exothermal polymerisation reaction to reach peaktemperatures of ca 277° C. after which it was cooled to approximately206° C. The subsequent 2^(nd) and 3^(rd) peak reaction temperatures were270° C. and 249° C. respectively with a cooling in between to 217° C.The reaction mixture was depressurised by a kick valve, cooled andpolymer “Comp. pol. 1” was separated from unreacted gas.

The Polymer Composition and the Cable

Formulations, i.e. the polymer composition from which layer(s),comprised in the cable in accordance with the present invention, is/areobtained using the polyethylene as described herein and crosslinkingagent, and comparative examples, have been prepared on lab scale andcompared, see Table 1. The crosslinking agent was added to thepolyethylene by distributing the crosslinking agent (crosslinking agentis in a liquid form) at 70° C. onto the polyethylene pellets. The wetpellets were kept at 80° C. until the pellets became dry. The amount ofcrosslinking agent, e.g. peroxide, was selected for each polymer, i.e.“Inv. pol.” 1-2, and “Comp. pol. 1”, so that about the same crosslinkingdegree as measured by the method for Hot Set Determination (with a loadof 20 N/cm²) was achieved.

Polymer pellets, i.e. said polymer composition, using the polyethyleneas described herein, and crosslinking agent were used to produce 10 kVcables, i.e. cable cores, on a Maillefer pilot cable line of CCV type.The cables have 3.4 mm nominal insulation thickness (the innersemiconducting layer is 1.0 mm thick and the outer semiconducting layeris 1.0 mm thick). The conductor cross section was 50 mm² strandedaluminium. The cable was produced by extrusion via a triple head. Thesemiconducting material used as inner and outer semiconducting materialwas LE0592 (a commercially semiconducting material supplied byBorealis). The cable cores, i.e. the cable comprising layer(s) andcomparative cable comprising layer(s), were produced with a line speedof 5.76 m/min when the peroxide used in the insulation layer was TBCPand with a line speed of 5.2 m/min when the peroxide used in theinsulation layer was Trigonox® 145-E85 (T145E85).

The content of volatile peroxide decomposition products, here methane,is measured according to the method for GC-Analysis, and is determinedby GC on a pie shaped sample specimen with a weight of 5 g. The pieshaped sample specimen is cut from a cable comprising crosslinkedlayer(s), i.e. from the cable according to the present invention andfrom a comparative cable. I.e. the sample specimen is cut fromcrosslinked layer(s) from a crosslinked and cooled cable. The samplespecimen comprises both insulation and semiconducting layers.

For hot set elongation determination, i.e. the method for Hot SetDetermination, samples are taken from the middle of the insulation layerof the cable core, i.e. from the crosslinked cable according to thepresent invention and also from a crosslinked comparative cable. I.e. adumbbell of a test material, i.e. of the hot set elongationdetermination samples, is equipped with a weight corresponding to 20N/cm².

TABLE 1 Inv. Ex 1 Inv. Ex. 2 Comp. Ex. 1 Polymer used Inv. pol. 1 Inv.pol. 2 Comp. pol. 1 in insulation Vinyl (P) 0.89 1.33 0.71 MFR2 (g/10min) 0.92 0.94 0.68 Pox 0.4 wt % 0.25 wt % 0.6 wt % Insulation T145E85TBCP TBCP Semicon LE0592 LE0592 LE0592 Hot Set 93.7 117.8 81.9elongation (%) Methane (ppm) 177 179 262

The examples surprisingly show that layer(s) of the cable in accordancewith the present invention, wherein the layer(s) is/are obtained fromthe polymer composition, reach excellent crosslinking levels (<175% hotset elongation) while forming <200 ppm of methane. The comparativeexamples all form more than 200 ppm of methane when crosslinked to atechnically equivalent level. Thus, polymer compositions of the presentinvention, wherein the polymer composition contains a total amount ofvinyl groups which is B vinyl groups per 1000 carbon atoms and comprisesa crosslinking agent in an amount which is Z wt %, are especiallysuitable for end applications where there is a need of a systemcombining a highly crosslinked system with the simultaneous formation oflittle volatile decomposition products, typically methane. Accordingly,a highly crosslinked system is surprisingly achieved even when acomparatively small amount of crosslinking agent, for example, peroxide,e.g., TBCP or T145E85, is used in accordance with the present inventionin the polymer composition containing a total amount of vinyl groupswhich is B vinyl groups per 1000 carbon atoms. Thus, with comparativelylow amount of TBCP or T145E85, i.e. the crosslinking agent in an amountof Z≤Z₂, wherein Z₂ is 0.60, used surprisingly good crosslinking levelsmeasured by hot set (≤100% hot set elongation) are achieved by thepolymer compostions of the present invention. In contrast, thecomparative polymer compositions, containing a lower total amount ofvinyl groups, need at least 0.6 wt % of the crosslinking agent, hereTBCP or T145E85, to achieve sufficient crosslinking levels leading toformation of more volatile decomposition products, typically methane.

Further, the cable, according to the present invention, with layerobtained from said polymer composition has unexpectedly also been shownto exhibit surprisingly low methane levels during crosslinking, while,at the same time, a technically desirable level of crosslinking degree,of the cable, is maintained using said relatively low amount of thecrosslinking agent, i.e. Z wt %, as defined herein. The crosslinkingagent may, e.g., be peroxides, which are well known in the art.

Moreover, the cable according to the present invention with layerobtained from the polymer composition wherein the polymer compositioncontains the comparably higher total amount of vinyl groups, B,surprisingly combines, in one polymer composition, good processability,e.g. flowability linked to a higher MFR₂, with excellent saggingresistance generally only associated with materials having a comparablylower MFR₂.

The invention claimed is:
 1. A cable comprising layer(s), wherein thelayer(s), is/are obtained from a polymer composition, wherein thepolymer composition comprises: a polyethylene and a crosslinking agent,characterized in that: the polymer composition contains a total amountof vinyl groups which is B vinyl groups per 1000 carbon atoms, and B₁≤B,wherein B₁ is 0.88, when measured prior to crosslinking according tomethod ASTM D6248-98; and the crosslinking agent is present in an amountwhich is Z wt %, prior to crosslinking, based on the total amount (100wt %) of the polymer composition, and Z≤−Z₂, wherein Z₂ is 0.60; whereinsaid layer(s) is/are crosslinked, and the decomposition of thecrosslinking agent during the crosslinking results in a content of lessthan 200 ppm of methane, and said crosslinked layer(s) has/have a hotset elongation, with a load of 20 N/cm², which is less than 175%.
 2. Thecable of claim 1, wherein the polyethylene is unsaturated.
 3. The cableof claim 1, wherein B₁ is 0.90.
 4. The cable of claim 1, wherein Z₂ is0.58, 0.56, 0.54, 0.52, 0.50, 0.48, 0.46, 0.44, 0.42 or 0.40.
 5. Thecable of claim 1, wherein said layer(s) is/are crosslinked and has/havea hot set elongation, with a load of 20 N/cm², which is less than 130%.6. The cable of claim 1, wherein the polyethylene is an unsaturated LDPEpolymer.
 7. The cable of claim 1, wherein the polyethylene is acopolymer of: a monomer, at least one polyunsaturated comonomer, andzero or one or more other comonomer(s), and wherein said total amount ofvinyl groups (B) present in the polymer composition include vinyl groupsoriginating from said at least one polyunsaturated comonomer.
 8. Thecable of claim 1, wherein the polyethylene is a copolymer of a monomerwith at least one polyunsaturated comonomer, wherein the polyunsaturatedcomonomer is a straight carbon chain with at least 8 carbon atoms, atleast two non-conjugated double bonds of which at least one is terminal,and at least 4 carbon atoms between the non-conjugated double bonds. 9.The cable of claim 1, wherein the polyethylene is a copolymer ofethylene and 1,7-octadiene.
 10. The cable of claim 1, wherein thepolyethylene is a low density polyethylene (LDPE) homopolymer orcopolymer.
 11. The cable of claim 1, wherein B≤B₂ and B₂ is 3.0 andZ₁≤Z≤Z₂, wherein Z₁ is 0.01.
 12. The cable of claim 1, wherein B₁ is0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25 or 1.30.
 13. The cable of claim1, wherein the polyethylene contains a total amount of vinyl groupswhich is P vinyl groups per 1000 carbon atoms, wherein P₁≤P≤P₂ and P₁ is0.89 and P₂ is 3.0.
 14. The cable of claim 13, wherein the polymercomposition simultaneously satisfies the following: P₁≤P≤P₂ wherein P₁is 0.89 and P₂ is 3.0; Z₁≤Z≤Z₂ wherein Z₁ is 0.15 and Z₂ is 0.60; andwherein the polymer composition has a melt flow rate, MFR₂, which is Ag/10 min and A₁≤A≤A₂ wherein A₁ is 0.15 and A₂ is 3.0.
 15. The cable ofclaim 13, wherein the polymer composition simultaneously satisfies thefollowing: P₁≤P≤P₂ wherein P₁ is 0.9 and P₂ is 1.5; Z₁≤Z≤Z₂ wherein Z₁is 0.25 and Z₂ is 0.50; and wherein the polymer composition has a meltflow rate, MFR₂, which is A g/10 min and A₁≤A≤A₂ wherein A₁ is 0.60 andA₂ is 2.5.
 16. The cable of claim 1, wherein the crosslinking agentcomprises a peroxide.
 17. The cable of claim 1, wherein the cable is apower cable.
 18. A process for producing the cable of claim
 1. 19. Theprocess of claim 18, wherein said cable is a power cable and whereinsaid process comprises the steps of: a₀) meltmixing the polymercomposition, optionally together with further components; and a)applying the meltmix obtained from step a₀) on a conductor to form atleast one cable layer.
 20. The process of claim 19, wherein said cableis a crosslinked power cable and wherein said process further comprisesthe step of: b) crosslinking the at least one cable layer obtained fromstep a).